Biomolecules

Topic: Enzymes; Subtopic: Structure and Function of Enzymes

Keyword Definitions:

• Enzyme: Biological catalyst that speeds up biochemical reactions without being consumed.

• Cofactor: Non-protein chemical compound required for enzyme activity.

• Coenzyme: Organic molecule serving as a transient carrier of specific atoms or functional groups in enzyme-catalyzed reactions.

• Apoenzyme: The protein part of an enzyme without its cofactor, inactive until combined with it.

• Prosthetic group: Tightly bound non-protein component essential for enzyme activity.

Lead Question (2025):
The protein portion of an enzyme is called:
(1) Cofactor
(2) Coenzyme
(3) Apoenzyme
(4) Prosthetic group

Explanation: The protein part of an enzyme, devoid of its non-protein cofactor, is known as the **apoenzyme**. It is catalytically inactive alone but becomes active upon binding with its cofactor, forming a holoenzyme. Apoenzymes determine enzyme specificity and are crucial for the catalytic process. Hence, the correct answer is (3) Apoenzyme.

1. Which of the following correctly describes the complete enzyme including its cofactor?
(1) Apoenzyme
(2) Holoenzyme
(3) Coenzyme
(4) Isoenzyme

Explanation: When an apoenzyme combines with its cofactor, it forms a catalytically active enzyme known as a **holoenzyme**. The apoenzyme provides specificity, while the cofactor enables catalysis. Together, they function efficiently in metabolic pathways. Therefore, the correct answer is (2) Holoenzyme.

2. The non-protein organic part of an enzyme which is loosely attached is called:
(1) Prosthetic group
(2) Coenzyme
(3) Apoenzyme
(4) Metal ion

Explanation: A **coenzyme** is an organic, non-protein molecule that temporarily associates with an enzyme to assist catalysis. Unlike prosthetic groups, coenzymes bind loosely and may be released after the reaction. Vitamins often serve as precursors of coenzymes. Hence, the correct answer is (2) Coenzyme.

3. Which among the following enzymes requires a metal ion as a cofactor?
(1) Carbonic anhydrase
(2) Urease
(3) Catalase
(4) Sucrase

Explanation: **Carbonic anhydrase** requires Zn²⁺ as a cofactor for its catalytic action. The zinc ion helps in the reversible hydration of carbon dioxide, forming carbonic acid. Enzymes depending on metal ions are called metalloenzymes. Therefore, the correct answer is (1) Carbonic anhydrase.

4. An enzyme and its substrate form a temporary complex called:
(1) Holoenzyme
(2) Enzyme-substrate complex
(3) Apoenzyme
(4) Coenzyme complex

Explanation: During catalysis, the substrate binds to the enzyme’s active site forming an **enzyme-substrate complex**. This interaction lowers activation energy, allowing the reaction to proceed faster. Once the product is formed, it is released and the enzyme remains unchanged. Hence, the correct answer is (2) Enzyme-substrate complex.

5. Which of the following statements about enzymes is correct?
(1) Enzymes increase activation energy
(2) Enzymes are consumed in reactions
(3) Enzymes lower activation energy
(4) Enzymes change equilibrium of reactions

Explanation: **Enzymes lower the activation energy** required for chemical reactions by stabilizing transition states. This increases reaction rate without altering the equilibrium or being consumed. They function under mild physiological conditions. Hence, the correct answer is (3) Enzymes lower activation energy.

6. Which of the following correctly represents the inactive form of an enzyme?
(1) Zymogen
(2) Holoenzyme
(3) Apoenzyme
(4) Isoenzyme

Explanation: Many enzymes are synthesized in an inactive precursor form called **zymogen** or proenzyme. They require biochemical modification, such as cleavage of peptide bonds, to become active. This mechanism prevents unwanted enzymatic activity within cells. Hence, the correct answer is (1) Zymogen.

Assertion–Reason Type Question

7. Assertion (A): Apoenzyme alone is catalytically inactive.
Reason (R): Apoenzyme requires a cofactor to form the active holoenzyme.
(1) Both A and R are true, and R is the correct explanation of A.
(2) Both A and R are true, but R is not the correct explanation of A.
(3) A is true, R is false.
(4) A is false, R is true.

Explanation: The **apoenzyme** lacks its cofactor and cannot catalyze reactions until combined with it to form a holoenzyme. Therefore, both statements are true, and R correctly explains A. Hence, the correct answer is (1) Both A and R are true, and R is the correct explanation of A.

Matching Type Question

8. Match the following enzymes with their cofactors:
List I (Enzyme) – List II (Cofactor)
A. Carbonic anhydrase  1. Cu²⁺
B. Urease  2. Zn²⁺
C. Cytochrome oxidase  3. Ni²⁺
D. Catalase  4. Fe³⁺

(1) A–2, B–3, C–1, D–4
(2) A–1, B–4, C–2, D–3
(3) A–3, B–2, C–4, D–1
(4) A–4, B–1, C–3, D–2

Explanation: Carbonic anhydrase uses Zn²⁺, urease uses Ni²⁺, cytochrome oxidase uses Cu²⁺, and catalase requires Fe³⁺ for activity. These cofactors are essential for catalytic reactions. Therefore, the correct matching is A–2, B–3, C–1, D–4, corresponding to option (1).

Fill in the Blanks Question

9. The complete, catalytically active enzyme consisting of an apoenzyme and its cofactor is called __________.
(1) Isoenzyme
(2) Holoenzyme
(3) Zymogen
(4) Allosteric enzyme

Explanation: The combination of an apoenzyme and its cofactor forms a **holoenzyme**, the active form capable of catalyzing reactions. The cofactor provides essential chemical groups or ions, while the apoenzyme offers substrate specificity. Hence, the correct answer is (2) Holoenzyme.

Choose the Correct Statements (Statement I & II)

10. Statement I: Apoenzyme combines with cofactor to form holoenzyme.
Statement II: Cofactor is always a metal ion.
(1) Both statements are true.
(2) Both statements are false.
(3) Statement I true, Statement II false.
(4) Statement I false, Statement II true.

Explanation: **Statement I is true** because an apoenzyme forms a holoenzyme upon binding with its cofactor. **Statement II is false**, as cofactors may be metal ions or organic coenzymes. Hence, the correct answer is (3) Statement I true, Statement II false.

Topic: Structure and Function of Nucleotides; Subtopic: Components of Nucleic Acids

Keyword Definitions:
• Nucleotide: Basic structural unit of nucleic acids, composed of a nitrogen base, a sugar, and a phosphate group.
• Nucleoside: Combination of a nitrogen base and a sugar, without a phosphate group.
• Amino acid: Organic compound containing amino and carboxyl groups, serving as the building blocks of proteins.
• Nitrogen base: Purine or pyrimidine component that pairs to form the genetic code in DNA or RNA.
• Adenine: A purine nitrogen base found in both DNA and RNA.

Lead Question - 2025

List I with List II:

List I        List II
A. Adenosine        I. Nitrogen base
B. Adenylic acid        II. Nucleotide
C. Adenine        III. Nucleoside
D. Alanine        IV. Amino acid

Choose the option with all correct matches

(1) A-III, B-IV, C-II, D-I
(2) A-III, B-II, C-IV, D-I
(3) A-III, B-II, C-I, D-IV
(4) A-II, B-III, C-I, D-IV

Explanation: Adenosine is a nucleoside formed by adenine and ribose. Adenylic acid (AMP) is a nucleotide containing adenine, ribose, and phosphate. Adenine is a nitrogen base, and alanine is an amino acid found in proteins. Therefore, the correct matches are A–III, B–II, C–I, and D–IV. Hence, the correct answer is (3). Nucleotides form nucleic acids, while amino acids form proteins, both essential for life processes.

1. Which of the following components form a nucleotide?
(1) Sugar + Base
(2) Sugar + Base + Phosphate
(3) Base + Phosphate
(4) Sugar + Phosphate
Explanation: A nucleotide consists of a nitrogen base, a pentose sugar, and one or more phosphate groups. This structure makes it the monomeric unit of nucleic acids, participating in genetic coding and energy transfer reactions like ATP. The correct answer is (2). Each nucleotide is linked by phosphodiester bonds forming DNA/RNA chains.

2. Which of the following bases is not found in RNA?
(1) Uracil
(2) Adenine
(3) Thymine
(4) Cytosine
Explanation: RNA contains adenine, uracil, cytosine, and guanine. Thymine is absent in RNA and replaced by uracil. This distinction helps differentiate DNA and RNA molecules during transcription and translation processes. Therefore, the correct answer is (3). DNA uses thymine, while RNA uses uracil for complementary base pairing.

3. Which type of bond links nucleotides in a nucleic acid chain?
(1) Hydrogen bond
(2) Ionic bond
(3) Phosphodiester bond
(4) Peptide bond
Explanation: Adjacent nucleotides in a nucleic acid chain are connected through phosphodiester bonds between the 3′ hydroxyl group of one sugar and the 5′ phosphate of the next. These covalent bonds provide backbone stability to DNA and RNA. The correct answer is (3). Hydrogen bonds occur between complementary bases, not between nucleotides.

4. The sugar in DNA is
(1) Ribose
(2) Deoxyribose
(3) Glucose
(4) Fructose
Explanation: DNA contains deoxyribose sugar, lacking one oxygen atom at the 2′ carbon compared to ribose in RNA. This difference gives DNA greater stability for long-term genetic storage. The correct answer is (2). Deoxyribose combines with phosphate and bases to form the double helical structure of DNA, discovered by Watson and Crick.

5. In DNA, adenine pairs with
(1) Cytosine
(2) Thymine
(3) Guanine
(4) Uracil
Explanation: In DNA, adenine pairs specifically with thymine through two hydrogen bonds, following Chargaff’s base pairing rule. This complementary pairing ensures genetic stability and accurate replication. The correct answer is (2). In RNA, adenine pairs with uracil instead of thymine, maintaining the same purine–pyrimidine pairing ratio.

6. The base sequence in DNA that codes for a specific protein is called a
(1) Codon
(2) Anticodon
(3) Gene
(4) Chromosome
Explanation: A gene is a specific DNA segment containing information for the synthesis of a protein or RNA molecule. Codons are triplets in mRNA that direct amino acid sequence, while genes represent the full hereditary unit. The correct answer is (3). Genes regulate traits and biological processes through controlled expression.

7. Assertion-Reason Question:
Assertion (A): DNA replication is semiconservative.
Reason (R): In replication, one parental strand acts as a template for the formation of a new complementary strand.
(1) Both A and R are true and R is the correct explanation of A
(2) Both A and R are true but R is not the correct explanation of A
(3) A is true but R is false
(4) A is false but R is true
Explanation: DNA replication is semiconservative because each daughter DNA retains one parental strand and synthesizes a new one. Meselson and Stahl confirmed this experimentally using N15 labeling. Hence, both statements are true and R correctly explains A. The correct answer is (1).

8. Matching Type Question:
Match List I with List II:
List I     List II
A. Guanine     I. Purine
B. Cytosine     II. Pyrimidine
C. Ribose     III. Pentose sugar
D. Peptide bond     IV. Proteins
(1) A-I, B-II, C-III, D-IV
(2) A-II, B-I, C-IV, D-III
(3) A-I, B-III, C-II, D-IV
(4) A-II, B-I, C-III, D-IV
Explanation: Guanine and adenine are purines, while cytosine, thymine, and uracil are pyrimidines. Ribose is a pentose sugar in RNA, and peptide bonds link amino acids in proteins. Thus, the correct matches are A–I, B–II, C–III, and D–IV. The correct answer is (1).

9. Fill in the Blanks Question:
DNA is composed of __________ types of nitrogen bases.
(1) Two
(2) Three
(3) Four
(4) Five
Explanation: DNA contains four types of nitrogen bases: adenine, thymine, guanine, and cytosine. They pair in a specific pattern, A–T and G–C, forming the genetic code. These four bases store all hereditary information. Hence, the correct answer is (3). Their precise arrangement determines gene function and protein synthesis.

10. Choose the Correct Statements Question:
Statement I: DNA contains thymine, while RNA contains uracil.
Statement II: RNA is generally double-stranded in eukaryotic cells.
(1) Both statements are correct
(2) Both statements are incorrect
(3) Statement I is correct and Statement II is incorrect
(4) Statement I is incorrect and Statement II is correct
Explanation: DNA contains thymine as a base, whereas RNA replaces thymine with uracil. Most RNA molecules are single-stranded in eukaryotic cells, unlike the double-stranded DNA. Hence, the correct answer is (3). Structural and base differences distinguish their functions in protein synthesis and heredity.

Topic: Enzymes; Subtopic: Enzyme Classification and Catalysis

Keyword Definitions:
• Enzyme: A biological catalyst that speeds up chemical reactions.
• Substrate (S): The molecule upon which an enzyme acts.
• Transferase: Enzymes that catalyze the transfer of a specific group from one molecule to another.
• Ligase: Enzymes that join two molecules using ATP.

Lead Question - 2025
Name the class of enzyme that usually catalyze the following reaction:
S – G + S′ → S + S′ – G
Where, G is a group other than hydrogen, S is a substrate, and S′ is another substrate.

(1) Hydrolase
(2) Lyase
(3) Transferase
(4) Ligase

Explanation:
Transferases are enzymes that catalyze the transfer of functional groups such as methyl, amino, or phosphate groups between donor and acceptor molecules. In the given reaction, group G is transferred from one substrate (S) to another (S′), which is a hallmark function of transferases. Hydrolases catalyze hydrolysis, lyases remove groups forming double bonds, and ligases form new bonds with ATP. Hence, the correct answer is Transferase. This reaction type is essential in metabolism, biosynthesis, and signal transduction, helping in molecular rearrangement without direct energy input.

1. Which of the following is not a function of enzymes?
(1) Catalyze biochemical reactions
(2) Change equilibrium constant of a reaction
(3) Lower activation energy
(4) Increase rate of reaction

Explanation:
Enzymes increase the rate of biochemical reactions by lowering activation energy but do not alter the equilibrium constant. The equilibrium depends on thermodynamic properties of reactants and products. Enzymes only accelerate reaching equilibrium. Therefore, option (2) is correct. Enzymes are highly specific, reusable, and sensitive to temperature and pH. They form enzyme–substrate complexes and ensure cellular efficiency in metabolic pathways.

2. The enzyme DNA polymerase is classified under which category?
(1) Oxidoreductase
(2) Ligase
(3) Transferase
(4) Hydrolase

Explanation:
DNA polymerase catalyzes the addition of nucleotides to the growing DNA strand using a DNA template, transferring deoxyribonucleotide monophosphate groups. It thus belongs to the transferase category, specifically nucleotidyl transferase. Ligases join DNA fragments, oxidoreductases catalyze oxidation-reduction reactions, and hydrolases catalyze bond cleavage by water. Hence, the correct answer is (3) Transferase. This enzyme plays a vital role in replication and repair processes.

3. Which enzyme catalyzes the joining of two molecules using ATP?
(1) Lyase
(2) Ligase
(3) Hydrolase
(4) Transferase

Explanation:
Ligases catalyze the joining (ligation) of two molecules using energy derived from ATP hydrolysis. They are crucial in DNA replication, repair, and biosynthetic reactions. Lyases break bonds without hydrolysis, hydrolases use water to break bonds, and transferases move functional groups between molecules. Therefore, the correct answer is (2) Ligase. This enzyme helps form stable covalent bonds essential for cellular synthesis.

4. Which of the following statements about enzymes is correct?
(1) Enzymes change the overall ΔG of the reaction
(2) Enzymes increase the activation energy
(3) Enzymes speed up reactions without being consumed
(4) Enzymes permanently alter their structure during reaction

Explanation:
Enzymes accelerate biochemical reactions by lowering activation energy while remaining unchanged after catalysis. They do not alter ΔG (free energy change) or equilibrium. Instead, they stabilize the transition state. Thus, option (3) is correct. Enzymes exhibit specificity due to their active site structure, which precisely fits substrates. After catalysis, the enzyme is regenerated to act repeatedly.

5. Which factor does not affect enzyme activity?
(1) Temperature
(2) pH
(3) Pressure
(4) Light intensity

Explanation:
Enzyme activity is influenced by temperature, pH, substrate concentration, and inhibitors, but not directly by light intensity. Pressure may affect gaseous reactions but has little effect on enzymes in solution. Hence, the correct answer is (4) Light intensity. Enzymes denature at extreme conditions, and maintaining optimal pH and temperature ensures proper conformation and catalytic efficiency for metabolic reactions.

6. Which of the following statements is true for enzyme inhibition?
(1) Competitive inhibitors bind to active site
(2) Non-competitive inhibitors bind to substrate
(3) Competitive inhibitors alter enzyme shape
(4) Non-competitive inhibitors compete with substrate

Explanation:
Competitive inhibitors resemble the substrate and bind to the enzyme’s active site, blocking substrate access. Non-competitive inhibitors bind elsewhere, altering enzyme conformation. Thus, the correct answer is (1) Competitive inhibitors bind to active site. This inhibition can be overcome by increasing substrate concentration, maintaining metabolic control and preventing overproduction of biomolecules in cellular processes.

7. Assertion-Reason Type Question
Assertion (A): Enzymes are specific in action.
Reason (R): Each enzyme acts only on one type of substrate due to complementary active site shape.
(1) Both A and R are true and R explains A
(2) Both A and R are true but R does not explain A
(3) A is true but R is false
(4) A is false but R is true

Explanation:
Enzyme specificity arises because the active site has a unique 3D shape that fits only a specific substrate, forming an enzyme–substrate complex. Hence, both Assertion and Reason are true, and R correctly explains A. Therefore, option (1) is correct. This property maintains regulation and order in biochemical pathways, preventing unwanted reactions in living systems.

8. Matching Type Question
Match the following enzymes with their functions:

A. Oxidoreductase — (i) Transfer of electrons
B. Transferase — (ii) Transfer of functional groups
C. Hydrolase — (iii) Hydrolysis of bonds
D. Lyase — (iv) Addition/removal of groups without hydrolysis

(1) A–i, B–ii, C–iii, D–iv
(2) A–ii, B–i, C–iv, D–iii
(3) A–iii, B–iv, C–i, D–ii
(4) A–iv, B–iii, C–ii, D–i

Explanation:
Enzymes are classified based on reaction type: Oxidoreductases catalyze redox reactions (transfer of electrons), Transferases transfer functional groups, Hydrolases perform bond cleavage using water, and Lyases add or remove groups forming double bonds. Hence, the correct match is (1) A–i, B–ii, C–iii, D–iv. These classes together account for the major catalytic mechanisms in metabolism and biosynthesis.

9. Fill in the Blanks Question
The enzyme that catalyzes conversion of sucrose into glucose and fructose is __________.
(1) Maltase
(2) Sucrase
(3) Lactase
(4) Amylase

Explanation:
Sucrase (invertase) catalyzes the hydrolysis of sucrose into glucose and fructose. This enzyme acts on the α-1,2-glycosidic bond in sucrose. Hence, the correct answer is (2) Sucrase. It is present in intestinal mucosa and essential for sugar digestion. Deficiency leads to intolerance to sucrose-containing foods, causing gastrointestinal disturbances and energy absorption inefficiency.

10. Choose the Correct Statements Question
Statement I: Enzyme activity is measured in International Units (IU).
Statement II: One IU equals the amount of enzyme converting 1 micromole of substrate per minute.
(1) Both statements are correct
(2) Both statements are incorrect
(3) Only Statement I is correct
(4) Only Statement II is correct

Explanation:
Enzyme activity quantifies catalytic efficiency. One International Unit (IU) is defined as the amount of enzyme that catalyzes the conversion of 1 micromole of substrate per minute under defined conditions. Therefore, both statements are correct, making option (1) correct. Measuring enzyme activity helps in enzyme kinetics, diagnostics, and biotechnology applications to assess metabolic health and efficiency.

Topic: Nucleic Acids; Subtopic: RNA World Hypothesis and Evolution of DNA

Keyword Definitions:
• RNA World: The hypothesis that RNA was the first genetic material capable of storing information and catalyzing reactions.
• Genetic Material: Molecules responsible for storing and transmitting hereditary information (DNA or RNA).
• Catalyst: A substance that increases the rate of a biochemical reaction without being consumed.
• DNA: Deoxyribonucleic acid, a stable double-stranded molecule storing genetic information in all living organisms except some viruses.
• Double Helix: The twisted-ladder structure of DNA formed by complementary base pairing.
• Repair Mechanism: Cellular process that corrects errors or damages in DNA to maintain genetic stability.

Lead Question – 2025
Given below are two statements:
Statement – I: In the RNA world, RNA is considered the first genetic material evolved to carry out essential life processes. RNA acts as a genetic material and also as a catalyst for some important biochemical reactions in living systems. Being reactive, RNA is unstable.
Statement – II: DNA evolved from RNA and is a more stable genetic material. Its double helical strands being complementary, resist changes by evolving repairing mechanism.
In the light of the above statements, choose the most appropriate answer from the options given below:
(1) Both statements I and statement II are correct
(2) Both statement I and statement II are incorrect
(3) Statement I is correct but statement II is incorrect
(4) Statement I is incorrect but statement II is correct

Explanation:
Both statements I and II are correct. The RNA world hypothesis suggests that RNA acted as the first genetic material capable of both storing genetic information and catalyzing reactions. However, due to its instability, DNA evolved as a more stable molecule. DNA’s complementary strands and repair systems ensure greater genetic fidelity and evolutionary advantage.

1. Which among the following proves that RNA could have been the first genetic material?
(1) RNA can store information and act as an enzyme
(2) RNA is double-stranded and stable
(3) RNA cannot act as an enzyme
(4) RNA is chemically inert
Explanation: RNA can act both as a genetic material and as a catalyst (ribozyme). This dual function supports the RNA world hypothesis, suggesting that RNA preceded DNA and proteins in evolution. RNA’s catalytic nature enabled early biochemical reactions essential for life formation, even before DNA or enzymes evolved.

2. Which type of RNA acts as a template during protein synthesis?
(1) mRNA
(2) tRNA
(3) rRNA
(4) snRNA
Explanation: Messenger RNA (mRNA) carries genetic information from DNA to the ribosome, where it serves as a template for protein synthesis. The sequence of nucleotides in mRNA determines the sequence of amino acids, ensuring proper translation of genetic information into functional proteins.

3. Which enzyme is responsible for catalyzing DNA synthesis from an RNA template?
(1) DNA polymerase
(2) RNA polymerase
(3) Reverse transcriptase
(4) Ligase
Explanation: Reverse transcriptase synthesizes DNA from an RNA template. It is found in retroviruses such as HIV. This enzyme supports the idea that RNA could have preceded DNA, as it demonstrates that RNA can serve as a template for the evolution of DNA, leading to more stable genetic storage systems.

4. Which of the following gives DNA its greater stability compared to RNA?
(1) Presence of uracil
(2) Presence of thymine and deoxyribose
(3) Presence of ribose sugar
(4) Lack of phosphodiester bonds
Explanation: DNA’s stability arises from the presence of thymine instead of uracil and deoxyribose instead of ribose. Deoxyribose lacks an oxygen atom at the 2′ position, making DNA less reactive and more stable. This chemical property allows DNA to serve as the long-term genetic material in living organisms.

5. Which of the following statements about DNA and RNA is incorrect?
(1) DNA contains thymine, RNA contains uracil
(2) DNA is single-stranded, RNA is double-stranded
(3) Both DNA and RNA contain adenine and guanine
(4) DNA has deoxyribose sugar while RNA has ribose sugar
Explanation: Option (2) is incorrect. DNA is typically double-stranded, while RNA is usually single-stranded. Their difference in sugars and bases makes RNA more reactive but less stable, and DNA more suited for hereditary information storage due to its stable double-helical structure and repair mechanisms.

6. In DNA, adenine pairs with thymine through:
(1) One hydrogen bond
(2) Two hydrogen bonds
(3) Three hydrogen bonds
(4) Phosphodiester bonds
Explanation: In DNA, adenine pairs with thymine through two hydrogen bonds, while cytosine pairs with guanine via three hydrogen bonds. These complementary base pairings ensure genetic fidelity during replication and transcription processes, making DNA a reliable molecule for long-term genetic information storage.

7. Assertion-Reason Type:
Assertion (A): DNA is more stable than RNA.
Reason (R): DNA lacks the 2'-hydroxyl group present in RNA.
(1) Both A and R are true and R is the correct explanation of A
(2) Both A and R are true but R is not the correct explanation of A
(3) A is true but R is false
(4) A is false but R is true
Explanation: Both A and R are true and R correctly explains A. DNA’s deoxyribose lacks a hydroxyl group at the 2′ position, reducing chemical reactivity and enhancing stability. This chemical difference ensures DNA’s resistance to hydrolysis and allows it to serve as a stable genetic material.

8. Matching Type:
Match the following:
A. mRNA    1. Carries amino acids
B. tRNA    2. Template for protein synthesis
C. rRNA    3. Forms ribosomal structure
(1) A–2, B–1, C–3
(2) A–3, B–2, C–1
(3) A–1, B–3, C–2
(4) A–2, B–3, C–1
Explanation: The correct match is A–2, B–1, C–3. mRNA serves as the template for protein synthesis, tRNA brings amino acids to the ribosome, and rRNA forms the structural and catalytic part of ribosomes. Together, they coordinate the translation process of gene expression efficiently.

9. Fill in the Blank:
DNA replication proceeds in the ______ direction.
(1) 3′ → 5′
(2) 5′ → 3′
(3) Random
(4) Both directions equally
Explanation: DNA replication occurs in the 5′ → 3′ direction. DNA polymerase adds nucleotides only to the 3′ end of the growing strand. The leading strand is synthesized continuously, while the lagging strand is synthesized discontinuously as Okazaki fragments, ensuring accurate and semiconservative DNA replication.

10. Choose the Correct Statements (Statement I & II):
Statement I: RNA can catalyze certain biochemical reactions.
Statement II: DNA can act as an enzyme in metabolic reactions.
(1) Both statements are correct
(2) Statement I is correct, Statement II is incorrect
(3) Both statements are incorrect
(4) Statement I is incorrect, Statement II is correct
Explanation: Statement I is correct while Statement II is incorrect. Some RNA molecules (ribozymes) possess catalytic activity, playing roles in RNA splicing and peptide bond formation. DNA, however, is chemically stable and does not exhibit catalytic activity. This further supports RNA’s ancient biological significance.

Subtopic: Reductionist Approach in Biology

Keyword Definitions:
• Reductionist Biology: Study of living systems by breaking them into simpler components.
• Holistic Biology: Approach that studies living organisms as complete systems.
• Physico-chemical approach: Analysis based on physical and chemical principles.
• Organism: An individual life form capable of growth and reproduction.
• Biological organization: Hierarchical structure from molecules to ecosystems.
• Metabolism: Sum of all biochemical reactions in a living organism.

Lead Question - 2025
Which one of the following statements refers to Reductionist Biology?
(1) Physico-chemical approach to study and understand living organisms
(2) Physiological approach to study and understand living organisms
(3) Chemical approach to study and understand living organisms
(4) Behavioural approach to study and understand living organisms

Explanation:
Reductionist Biology explains life by analyzing its simplest physico-chemical and molecular aspects. It focuses on how complex biological phenomena emerge from chemical and physical interactions of molecules and cells. This approach has contributed greatly to molecular biology and biochemistry. Hence, the correct answer is (1) Physico-chemical approach to study and understand living organisms.

1. Which of the following is an example of Reductionist Biology?
(1) Study of DNA replication using enzymes
(2) Observation of animal behavior
(3) Study of ecology of forests
(4) Study of evolution of species
Explanation:
Reductionist Biology involves breaking complex systems into smaller parts for detailed analysis. Studying DNA replication using enzymes represents this molecular-level approach. It focuses on biochemical mechanisms rather than the organism as a whole. Thus, the correct answer is (1) Study of DNA replication using enzymes.

2. Which of the following is a Holistic approach example?
(1) Study of enzyme kinetics
(2) Study of photosynthesis in isolated chloroplasts
(3) Study of an entire ecosystem
(4) Analysis of protein folding
Explanation:
The holistic approach studies living systems in totality, focusing on interactions within the entire system. The study of an ecosystem includes all organisms, abiotic factors, and their relationships, representing a complete picture of life processes. Hence, (3) Study of an entire ecosystem is correct.

3. The holistic approach in biology emphasizes
(1) Interaction of parts within a system
(2) Isolated study of cell components
(3) Molecular study of enzymes
(4) Analysis of atomic structure
Explanation:
The holistic approach stresses understanding the interdependence and integration of biological components within a system. It focuses on how the combined functioning of organs and organisms contributes to life. Hence, the correct answer is (1) Interaction of parts within a system.

4. Who proposed that life can be explained through physico-chemical principles?
(1) Darwin
(2) Mendel
(3) Schwann
(4) Wohler
Explanation:
Friedrich Wohler demonstrated in 1828 that urea could be synthesized from inorganic compounds, proving that organic molecules could arise from physical and chemical reactions. This finding laid the foundation of the reductionist concept in biology. Thus, the correct answer is (4) Wohler.

5. Which of the following best describes the holistic view of biology?
(1) Analysis of molecular components only
(2) Understanding interactions between biological systems
(3) Studying structure of DNA
(4) Measuring enzyme activity
Explanation:
Holistic biology emphasizes that living organisms are more than the sum of their parts. It studies how systems and their components interact to produce emergent properties of life. Therefore, the correct answer is (2) Understanding interactions between biological systems.

6. Which of the following statements is NOT true about Reductionist Biology?
(1) It helps in understanding molecular basis of life
(2) It involves dividing systems into parts for study
(3) It neglects interactions between components
(4) It considers the system as a whole
Explanation:
Reductionist Biology focuses on breaking down living systems into smaller parts to understand their functioning but often overlooks the holistic interactions. It does not consider the system as a whole, making option (4) incorrect about reductionist approach. Hence, the correct answer is (4).

Assertion-Reason Question
7. Assertion (A): Reductionist Biology focuses on studying biological systems at molecular and cellular levels.
Reason (R): The holistic approach ignores molecular studies.
(1) Both A and R are true, and R is the correct explanation of A.
(2) Both A and R are true, but R is not the correct explanation of A.
(3) A is true, but R is false.
(4) A is false, but R is true.
Explanation:
Reductionist Biology indeed studies life processes at molecular and cellular levels. However, the holistic approach does not ignore molecular studies but rather integrates them into a system-wide understanding. Hence, A is true, R is false. Correct answer: (3).

Matching Type Question
8. Match the following approaches with their features:
A. Reductionist Biology
B. Holistic Biology
C. Physiology
D. Ecology
List II – Features
(1) Studies whole system interaction
(2) Focus on biochemical pathways
(3) Studies organismal functions
(4) Focus on organism-environment relationship
(a) A–2, B–1, C–3, D–4
(b) A–3, B–2, C–4, D–1
(c) A–4, B–1, C–2, D–3
(d) A–1, B–2, C–3, D–4
Explanation:
Reductionist Biology focuses on biochemical details (2), Holistic Biology on overall system interaction (1), Physiology on functions of organisms (3), and Ecology on environmental relationships (4). Hence, the correct match is (a) A–2, B–1, C–3, D–4.

Fill in the Blanks Question
9. The ________ approach in biology considers the organism as a whole rather than a collection of parts.
(1) Chemical
(2) Reductionist
(3) Holistic
(4) Anatomical
Explanation:
The holistic approach considers the organism as an integrated whole, focusing on the interactions and interdependence of its components rather than individual parts. It provides a broader understanding of life functions. Hence, the correct answer is (3) Holistic.

Choose the Correct Statements Question
10. Statement I: Reductionist Biology simplifies complex biological systems for analysis.
Statement II: Holistic Biology studies parts without considering interrelations.
(1) Both statements are true
(2) Both statements are false
(3) Statement I is true, Statement II is false
(4) Statement I is false, Statement II is true
Explanation:
Reductionist Biology simplifies biological systems into components to understand underlying mechanisms, making Statement I true. Holistic Biology emphasizes interrelations among parts, so Statement II is false. Hence, the correct answer is (3).

Topic: Enzymes; Subtopic: Mechanism of Enzyme Action

Keyword Definitions:

• Enzyme: Biological catalyst that speeds up biochemical reactions without being consumed.

• Active site: Specific region on the enzyme where substrate molecules bind and react.

• Substrate: The reactant molecule upon which the enzyme acts.

• Enzyme-substrate complex: Temporary intermediate formed when enzyme binds to substrate.

• Induced fit model: Explains that substrate binding induces a conformational change in the enzyme to facilitate catalysis.

Lead Question - 2024 (Jhajjhar)

The catalytic cycle of an enzyme action is described as:

A. Enzyme releases products of the reaction and gets free.

B. Substrate induces the enzyme to alter its shape.

C. The substrate binds with the active site of the enzyme.

D. Enzyme-product complex is formed.

1. C → B → A → D

2. C → B → D → A

3. B → C → D → A

4. D → C → A → B

Explanation:

The catalytic cycle begins when the substrate binds to the enzyme’s active site forming the enzyme-substrate complex. This induces structural changes (induced fit model), leading to catalysis and formation of the enzyme-product complex. The enzyme then releases the product and becomes free for reuse. Hence, the correct sequence is C → B → D → A. Enzymes function by lowering activation energy, ensuring rapid biochemical reactions in living cells.

1. The part of the enzyme where the substrate binds is called:

1. Allosteric site

2. Active site

3. Catalytic site

4. Binding site

Explanation:

The active site is the specific region of an enzyme where substrate molecules attach through weak bonds. It has a unique three-dimensional structure complementary to the substrate. The binding leads to the formation of the enzyme-substrate complex, initiating the catalytic reaction. Thus, the correct answer is active site.

2. Which one of the following statements is true about enzymes?

1. They alter the equilibrium of reaction.

2. They lower the activation energy of reaction.

3. They are consumed during reactions.

4. They act at any temperature.

Explanation:

Enzymes lower the activation energy of biochemical reactions without changing the equilibrium point. They speed up reactions by stabilizing the transition state. However, they are not consumed in the process. They function best at optimal pH and temperature. Hence, the correct answer is that enzymes lower activation energy of reactions.

3. Enzymes are made up of:

1. Lipids

2. Proteins

3. Carbohydrates

4. Vitamins

Explanation:

Most enzymes are proteins with a specific three-dimensional conformation essential for their catalytic activity. Some enzymes may also require non-protein cofactors or coenzymes for complete functionality. Protein enzymes can be denatured by heat or pH changes. Hence, the correct answer is proteins.

4. Which of the following models explains enzyme action more accurately?

1. Lock and key model

2. Induced fit model

3. Collision model

4. Random fit model

Explanation:

The induced fit model proposed by Koshland explains that enzyme shape slightly alters when substrate binds to form a perfect fit. This enhances catalytic efficiency. It replaced the older rigid lock and key model, emphasizing enzyme flexibility. Hence, the correct answer is induced fit model.

5. The enzyme that converts starch into maltose is:

1. Maltase

2. Amylase

3. Lactase

4. Sucrase

Explanation:

Amylase catalyzes the hydrolysis of starch into maltose and dextrins. It is secreted by salivary glands and pancreas. It initiates carbohydrate digestion by breaking α-1,4 glycosidic bonds. Hence, the correct answer is amylase, a key digestive enzyme in humans.

6. Which factor does not affect enzyme activity?

1. Temperature

2. pH

3. Substrate concentration

4. Atomic number

Explanation:

Enzyme activity depends on temperature, pH, and substrate concentration, but not on atomic number. Temperature affects enzyme conformation, and extreme pH can denature enzymes. Substrate concentration determines reaction rate until saturation. Hence, the correct answer is atomic number.

Assertion-Reason Type Question

7. Assertion (A): Enzyme action is highly specific.

Reason (R): Enzymes can catalyze reactions of any substrate.

1. Both (A) and (R) are correct, and (R) explains (A).

2. Both (A) and (R) are correct, but (R) does not explain (A).

3. (A) is correct, but (R) is incorrect.

4. (A) is incorrect, but (R) is correct.

Explanation:

Enzyme action is highly specific as each enzyme acts only on a particular substrate due to complementary shape and charge of its active site. Enzymes cannot catalyze reactions of any substrate. Thus, the assertion is correct but the reason is incorrect.

Matching Type Question

8. Match the following:

A. Urease — I. Hydrolysis of starch

B. Amylase — II. Hydrolysis of urea

C. Lipase — III. Breakdown of fats

1. A-II, B-I, C-III

2. A-I, B-II, C-III

3. A-III, B-I, C-II

4. A-II, B-III, C-I

Explanation:

Urease catalyzes the hydrolysis of urea into ammonia and CO₂. Amylase acts on starch to form maltose. Lipase breaks down lipids into fatty acids and glycerol. Hence, the correct match is A-II, B-I, C-III.

Fill in the Blanks Type Question

9. The enzyme which catalyzes the conversion of hydrogen peroxide into water and oxygen is ________.

1. Oxidase

2. Catalase

3. Hydrolase

4. Ligase

Explanation:

Catalase is an enzyme found in most aerobic organisms that decomposes toxic hydrogen peroxide into water and oxygen, preventing oxidative cell damage. It ensures cellular protection from reactive oxygen species. Hence, the correct answer is catalase.

Choose the Correct Statements (Statement I & II)

10. Statement I: Enzyme activity decreases beyond optimum temperature.

Statement II: High temperature denatures the enzyme protein.

1. Both statements are correct.

2. Both statements are incorrect.

3. Statement I is correct, but Statement II is incorrect.

4. Statement I is incorrect, but Statement II is correct.

Explanation:

Both statements are correct. Enzymes show maximum activity at their optimum temperature (usually 37°C in humans). Beyond this, heat denatures the protein structure of the enzyme, rendering it inactive. Therefore, enzyme activity declines at higher temperatures. 

Topic: Enzymes and Biological Molecules; Subtopic: Ribozyme, Lecithin, GLUT-4, Vitamins

Keyword Definitions:

• Ribozyme: An RNA molecule with catalytic activity capable of acting as an enzyme without proteins.

• Lecithin: A phospholipid that plays a vital role in fat metabolism and forms part of the cell membrane.

• GLUT-4: A glucose transporter protein found in adipose tissue and skeletal muscles, insulin-dependent.

• Vitamin: An organic compound essential in small amounts, often functioning as a coenzyme or precursor.

• Coenzyme: A non-protein organic molecule that binds temporarily with enzymes to assist catalysis.

• Lipid: Fat-like substances that are insoluble in water and form structural components of membranes.

• Enzyme: A biological catalyst that speeds up biochemical reactions without being consumed.

Lead Question - 2024 (Jhajjhar)

Match List-I with List-II:
List-I          List-II
A. Ribozyme          I. Glucose transport
B. Lecithin          II. Non proteinaceous enzyme
C. Glut-4          III. Lipid
D. Vitamins          IV. Coenzyme
Choose the correct answer from the options given below:

1. A-IV, B-III, C-I, D-II
2. A-IV, B-III, C-II, D-I
3. A-II, B-I, C-III, D-IV
4. A-II, B-III, C-I, D-IV

Explanation: Ribozyme is a non-protein enzyme (II), Lecithin is a lipid (III), GLUT-4 is a glucose transporter (I), and Vitamins act as coenzymes (IV). Hence, the correct match is A-II, B-III, C-I, D-IV. Ribozymes show catalytic activity, Lecithin supports cell membranes, GLUT-4 helps glucose uptake, and Vitamins function in metabolism.

1. Guessed Question: Which of the following acts as a non-protein enzyme?
1. Immunoglobulin
2. Ribozyme
3. Albumin
4. Hormone
Explanation: Ribozymes are catalytic RNA molecules functioning as enzymes without protein structure. They catalyze RNA splicing and peptide bond formation. This unique property supports the RNA world hypothesis. Hence, Ribozyme acts as a non-protein enzyme.

2. Guessed Question: GLUT-4 transporters are mainly found in:
1. Liver cells
2. Neurons
3. Skeletal muscles and adipose tissue
4. Erythrocytes
Explanation: GLUT-4 is an insulin-dependent glucose transporter present in skeletal muscles and adipose tissue. It facilitates glucose entry during insulin stimulation. This maintains blood glucose homeostasis. Therefore, option 3 is correct.

3. Guessed Question: Lecithin is a phospholipid that is structurally composed of:
1. Glycerol, fatty acids, phosphate, and choline
2. Ribose and phosphate only
3. Protein and carbohydrate
4. Cholesterol only
Explanation: Lecithin is a phospholipid comprising glycerol backbone, fatty acids, phosphate group, and choline. It forms cell membrane bilayers and aids in lipid metabolism. Hence, the correct answer is glycerol, fatty acids, phosphate, and choline.

4. Guessed Question: Vitamins acting as coenzymes participate mainly in:
1. Hormonal balance
2. Enzymatic reactions
3. Protein transport
4. Cell division
Explanation: Vitamins often act as coenzymes or their precursors in metabolic pathways. They assist enzymes in catalyzing biochemical reactions efficiently. For example, vitamin B₁ acts as thiamine pyrophosphate, a coenzyme in carbohydrate metabolism.

5. Guessed Question: Which vitamin acts as a coenzyme for transamination reactions?
1. Vitamin B₁₂
2. Vitamin B₆
3. Vitamin D
4. Vitamin C
Explanation: Vitamin B₆ (pyridoxine) acts as a coenzyme in transamination reactions by forming pyridoxal phosphate. It helps in amino acid metabolism and neurotransmitter synthesis. Therefore, the correct answer is Vitamin B₆.

6. Guessed Question: Identify the biomolecule acting as both structural and metabolic component:
1. Lecithin
2. Collagen
3. Hemoglobin
4. Insulin
Explanation: Lecithin is a phospholipid contributing structurally to the cell membrane and metabolically to lipid transport and emulsification. It stabilizes membranes and aids in fat digestion. Thus, Lecithin has dual functional importance.

7. Assertion-Reason Question:
Assertion (A): Ribozymes are RNA molecules showing catalytic activity.
Reason (R): They contain an active protein site responsible for catalysis.
1. Both A and R are true and R is the correct explanation
2. Both A and R are true but R is not the correct explanation
3. A is true but R is false
4. A is false but R is true
Explanation: Ribozymes are catalytic RNAs that function without proteins; their catalytic sites are RNA-based, not protein-based. Hence, A is true but R is false.

8. Matching Type Question:
Match the following enzymes with cofactors:
A. Carbonic anhydrase – (i) Zn²⁺
B. Hexokinase – (ii) Mg²⁺
C. Catalase – (iii) Fe³⁺
D. DNA polymerase – (iv) Mn²⁺
Options:
1. A-i, B-ii, C-iii, D-iv
2. A-iii, B-i, C-ii, D-iv
3. A-ii, B-iii, C-i, D-iv
4. A-i, B-ii, C-iv, D-iii
Explanation: Correct pairing is A-i, B-ii, C-iii, D-iv. Each enzyme requires specific metal cofactors for function. Carbonic anhydrase uses Zn²⁺, Hexokinase needs Mg²⁺, Catalase has Fe³⁺, and DNA polymerase is activated by Mn²⁺ ions.

9. Fill in the Blanks:
The glucose transporter that is insulin-dependent is _______.
1. GLUT-1
2. GLUT-2
3. GLUT-3
4. GLUT-4
Explanation: GLUT-4 is the insulin-dependent glucose transporter found in skeletal muscles and adipose tissue. It mediates glucose uptake after insulin binding. This mechanism maintains normal blood sugar levels and cellular energy balance.

10. Choose the Correct Statements (Statement I & Statement II):
Statement I: Vitamins act as enzymes for metabolic reactions.
Statement II: Vitamins act as coenzymes, assisting enzyme function.
1. Both statements are true
2. Both statements are false
3. Statement I is true, Statement II is false
4. Statement I is false, Statement II is true
Explanation: Vitamins themselves are not enzymes; they serve as coenzymes or precursors, supporting enzyme activity in metabolism. Therefore, Statement I is false, and Statement II is true.

Topic: Enzymes and Proteins; Subtopic: Types and Functions of Biomolecules

Keyword Definitions:

• Collagen: A structural protein found abundantly in connective tissues like tendons and skin.

• GLUT-4: A glucose transporter protein that mediates glucose uptake into muscle and fat cells.

• Trypsin: A digestive enzyme that breaks down proteins in the small intestine.

• RuBisCO: Ribulose-1,5-bisphosphate carboxylase/oxygenase, an enzyme involved in photosynthesis.

Lead Question - 2024 (Jhajjhar)

Match List-I with List-II
List-I          List-II
A. Collagen          I. Enzyme
B. GLUT-4          II. Most abundant enzyme in biosphere
C. Trypsin          III. Most abundant protein in animal world
D. RuBisCO          IV. Enables glucose transport into cells

1. A-III, B-I, C-IV, D-II
2. A-II, B-III, C-I, D-IV
3. A-III, B-IV, C-I, D-II
4. A-I, B-III, C-IV, D-II

Explanation: The correct answer is option 3 (A-III, B-IV, C-I, D-II). Collagen is the most abundant protein in animals, providing structural strength. GLUT-4 facilitates glucose entry into cells. Trypsin acts as a digestive enzyme, and RuBisCO is the most abundant enzyme in the biosphere responsible for carbon fixation during photosynthesis. These biomolecules ensure metabolic efficiency and structural integrity across organisms.

1. Which of the following enzymes catalyzes the breakdown of starch into maltose?
1. Maltase
2. Sucrase
3. Amylase
4. Lactase

Explanation: The correct answer is option 3 (Amylase). Amylase, secreted by salivary glands and pancreas, hydrolyzes starch into maltose and dextrins. It is essential for carbohydrate digestion. This enzyme functions optimally at near-neutral pH in the mouth and slightly alkaline conditions in the small intestine, facilitating efficient conversion of polysaccharides to disaccharides.

2. Which of the following bonds is broken during the denaturation of proteins?
1. Peptide bonds
2. Hydrogen bonds
3. Glycosidic bonds
4. Phosphodiester bonds

Explanation: The correct answer is option 2 (Hydrogen bonds). Denaturation involves the disruption of weak hydrogen and ionic interactions without breaking peptide bonds. This leads to loss of the native conformation and biological activity of proteins. Heat, pH changes, or chemicals like urea can induce denaturation, making proteins biologically inactive but chemically intact.

3. Which among the following enzymes is responsible for the conversion of fibrinogen to fibrin during blood clotting?
1. Pepsin
2. Trypsin
3. Thrombin
4. Amylase

Explanation: The correct answer is option 3 (Thrombin). Thrombin converts soluble fibrinogen into insoluble fibrin, forming a blood clot mesh. This conversion is a critical part of the coagulation cascade, preventing excessive bleeding after injury. The enzyme is produced from prothrombin by prothrombinase in the presence of calcium ions and clotting factors.

4. Assertion-Reason Question:
Assertion (A): RuBisCO is the most abundant enzyme in the biosphere.
Reason (R): It catalyzes the carboxylation of RuBP in the Calvin cycle during photosynthesis.
1. Both A and R are true, and R is the correct explanation of A
2. Both A and R are true, but R is not the correct explanation of A
3. A is true, R is false
4. A is false, R is true

Explanation: The correct answer is option 1. RuBisCO catalyzes the carboxylation of ribulose-1,5-bisphosphate (RuBP) to form 3-phosphoglycerate, a key step in photosynthetic carbon fixation. Due to its abundance in all photosynthetic organisms, RuBisCO is regarded as the most abundant enzyme in the biosphere, critical for sustaining life.

5. Match the following enzymes with their substrates:
A. Lipase - I. Urea
B. Urease - II. Lipids
C. Maltase - III. Maltose
D. Amylase - IV. Starch
1. A-II, B-I, C-III, D-IV
2. A-I, B-II, C-III, D-IV
3. A-III, B-IV, C-II, D-I
4. A-IV, B-III, C-I, D-II

Explanation: The correct answer is option 1 (A-II, B-I, C-III, D-IV). Lipase hydrolyzes lipids into fatty acids and glycerol. Urease breaks urea into ammonia and carbon dioxide. Maltase hydrolyzes maltose into glucose, while amylase breaks starch into maltose. These enzymes exemplify substrate specificity and biological efficiency in metabolism.

6. Which of the following is not a characteristic of enzymes?
1. They are specific in their action
2. They are consumed during the reaction
3. They lower activation energy
4. They act as biological catalysts

Explanation: The correct answer is option 2. Enzymes are not consumed during biochemical reactions; they act repeatedly as catalysts. They bind substrates, reduce activation energy, and accelerate reaction rates. After reaction completion, enzymes are regenerated unchanged, allowing them to catalyze multiple cycles without depletion, maintaining metabolic efficiency in living organisms.

7. Fill in the blanks:
_________ catalyzes the conversion of hydrogen peroxide into water and oxygen.
1. Peroxidase
2. Catalase
3. Oxidase
4. Reductase

Explanation: The correct answer is option 2 (Catalase). Catalase decomposes hydrogen peroxide (H₂O₂), a toxic by-product of metabolism, into harmless water and oxygen. Found in peroxisomes of eukaryotic cells, this enzyme protects tissues from oxidative damage and maintains redox homeostasis, making it one of the fastest enzymes known in biological systems.

8. Choose the correct statements:
Statement I: Pepsin works best in acidic pH.
Statement II: Trypsin functions optimally in alkaline pH.
1. Both statements are correct
2. Only Statement I is correct
3. Only Statement II is correct
4. Both statements are incorrect

Explanation: The correct answer is option 1. Pepsin, secreted in the stomach, is active in acidic pH (~2). Trypsin, secreted by the pancreas into the intestine, functions optimally in alkaline pH (~8). These adaptations ensure efficient protein digestion at different regions of the digestive tract, demonstrating enzyme pH specificity and physiological regulation.

9. Which enzyme helps in converting sucrose into glucose and fructose?
1. Invertase
2. Sucrase
3. Lactase
4. Zymase

Explanation: The correct answer is option 1 (Invertase). Invertase catalyzes the hydrolysis of sucrose into glucose and fructose, collectively called invert sugar due to optical rotation change. This enzyme is secreted by yeast and used in confectionery industries for producing soft-centered sweets, demonstrating industrial and biological significance of enzymatic reactions.

10. Which of the following statements about collagen is true?
1. It is an enzyme
2. It is a storage protein
3. It provides tensile strength to connective tissues
4. It is a hormone

Explanation: The correct answer is option 3. Collagen provides tensile strength and structural support to connective tissues such as tendons, ligaments, and skin. It is composed of three polypeptide chains forming a triple helix. This unique structure enables flexibility and durability, making collagen a key component of animal structural integrity and tissue repair.

Topic: Enzymes; Subtopic: Effect of pH on Enzyme Activity

Keyword Definitions:

• Enzyme: Biological catalyst that speeds up biochemical reactions by lowering activation energy.

• Active site: The specific region on the enzyme where substrate molecules bind and reactions occur.

• Optimum pH: The pH at which an enzyme exhibits maximum activity.

• Denaturation: Structural alteration of an enzyme leading to loss of function, often caused by extreme pH or temperature.

• Substrate: The molecule upon which an enzyme acts to form products.

Lead Question - 2024 (Jhajjhar)
Which of the following graphs explains the effect of pH on the enzyme activity?
Graph 1: Graph 1 shows a bell-shaped curve with enzyme activity on the y-axis and pH on the x-axis.
Graph 2: Graph 2 shows a bell-shaped curve with pH on the y-axis and enzyme activity on the x-axis.
Graph 3: Enzyme activity continuously increases and then plateaus as the pH increases.
Graph 4: Enzyme activity continuously increases and then plateaus as the pH increases.

Explanation:
The correct answer is Graph 1. Enzyme activity typically follows a bell-shaped curve when plotted against pH. Each enzyme has an optimum pH where its activity is maximum. Beyond this range, enzyme structure and active site configuration change due to denaturation, decreasing catalytic efficiency. For example, pepsin works best at acidic pH while trypsin at alkaline pH.

1. The optimum pH for pepsin is approximately:
1. 2
2. 5
3. 7
4. 9

Explanation:
Option 1 is correct. Pepsin, a digestive enzyme found in the stomach, has an optimum pH around 2. It functions best in the highly acidic environment created by hydrochloric acid. Deviations from this pH reduce its catalytic activity as changes in H+ concentration alter the ionization state of amino acids in the active site.

2. Which enzyme functions optimally at alkaline pH?
1. Pepsin
2. Trypsin
3. Amylase
4. Catalase

Explanation:
Option 2 is correct. Trypsin, secreted by the pancreas, works in the small intestine where the environment is slightly alkaline (pH 8). It digests proteins into smaller peptides. The enzyme’s tertiary structure is stable at this pH, while acidic conditions cause denaturation, leading to decreased activity or complete inactivation of the enzyme molecule.

3. When an enzyme is exposed to a very high pH, it:
1. Increases its activity
2. Becomes inactive due to denaturation
3. Remains unaffected
4. Converts into a substrate

Explanation:
Option 2 is correct. Extreme pH conditions disrupt ionic bonds and hydrogen bonds that maintain the enzyme’s tertiary structure. As a result, the enzyme becomes denatured, losing its specific shape and functional active site. Consequently, the substrate can no longer bind efficiently, and the enzyme’s catalytic activity declines or stops entirely.

4. Which of the following statements best explains the effect of pH on enzyme activity?
1. pH alters the enzyme concentration
2. pH affects the shape of the enzyme and active site
3. pH affects temperature
4. pH controls product formation directly

Explanation:
Option 2 is correct. pH modifies the ionization of amino acid residues within the enzyme, especially those forming the active site. This alteration changes the enzyme’s 3D structure, impacting substrate binding. Each enzyme has a specific pH optimum. Deviations either lower or raise H+ concentration, disrupting active site geometry and reducing catalytic efficiency.

5. The enzyme amylase shows maximum activity at:
1. pH 2
2. pH 5
3. pH 6.8
4. pH 9

Explanation:
Option 3 is correct. Salivary amylase, responsible for starch digestion in the mouth, works best around pH 6.8, which is nearly neutral. At very low or high pH values, its activity decreases because the enzyme’s structure is altered. This ensures that enzymatic reactions occur efficiently in specific physiological environments within the human body.

6. Enzyme activity generally decreases beyond optimum pH because:
1. Substrate concentration decreases
2. Active site changes due to altered ionization
3. Enzyme quantity reduces
4. Temperature increases

Explanation:
Option 2 is correct. Changes in pH alter the charge and ionization state of amino acid residues, particularly those in the active site. This leads to conformational changes in the enzyme, reducing substrate affinity and catalytic efficiency. Thus, beyond optimum pH, enzyme activity rapidly falls due to structural distortion or complete denaturation.

Assertion-Reason Type Question
7. Assertion (A): Each enzyme has an optimum pH.
Reason (R): At optimum pH, the enzyme’s active site is most suitable for substrate binding.
1. Both A and R are true, and R is the correct explanation of A.
2. Both A and R are true, but R is not the correct explanation of A.
3. A is true, R is false.
4. A is false, R is true.

Explanation:
Option 1 is correct. Every enzyme exhibits maximum activity at a specific pH called the optimum pH. At this value, the active site conformation and substrate binding capability are ideal, ensuring maximum catalytic efficiency. Any deviation changes the enzyme’s charge distribution, lowering substrate affinity and reaction rate, thereby decreasing enzymatic performance significantly.

Matching Type Question
8. Match the enzyme with its optimum pH:
A. Pepsin → i. 7
B. Trypsin → ii. 8
C. Amylase → iii. 6.8
D. Catalase → iv. 2
1. A-iv, B-ii, C-iii, D-i
2. A-i, B-iii, C-iv, D-ii
3. A-ii, B-iv, C-i, D-iii
4. A-iii, B-ii, C-i, D-iv

Explanation:
Option 1 is correct. Pepsin works best at pH 2, trypsin at pH 8, amylase at pH 6.8, and catalase at pH 7. Each enzyme functions optimally at a specific hydrogen ion concentration, reflecting its physiological environment. This precise adaptation ensures maximum efficiency in digestion and metabolism under varying body conditions.

Fill in the Blanks Question
9. The pH value at which an enzyme shows maximum activity is called ______.
1. Activation pH
2. Neutral pH
3. Optimum pH
4. Enzyme pH

Explanation:
Option 3 is correct. The optimum pH is the specific hydrogen ion concentration where an enzyme’s catalytic activity is highest. At this pH, the enzyme’s active site has the most suitable conformation for substrate binding. Extreme deviations in pH disturb active site ionization, altering enzyme shape and reducing catalytic efficiency in biochemical reactions.

Choose the Correct Statements Question
10. Statement I: All enzymes have the same optimum pH.
Statement II: Optimum pH varies depending on enzyme type and its environment.
1. Both statements are true.
2. Both statements are false.
3. Statement I is true, Statement II is false.
4. Statement I is false, Statement II is true.

Explanation:
Option 4 is correct. Optimum pH is not the same for all enzymes; it depends on their source and function. Pepsin acts best at acidic pH, while trypsin prefers alkaline conditions. Variation in enzyme structure, habitat, and function determine the specific pH range for maximum catalytic activity, ensuring physiological balance and efficiency.

Topic: Proteins and Secondary Metabolites; Subtopic: Plant-Derived Compounds and Their Functions

Keyword Definitions:

• Toxin: A poisonous substance produced by living organisms like plants, animals, or microbes that can harm other organisms.

• Polymeric substance: A large molecule made up of repeating monomer units, such as starch, cellulose, or gum.

• Lectin: A protein that binds specifically to carbohydrates and is often involved in cell recognition and defense mechanisms.

• Drug: A natural or synthetic compound used to diagnose, treat, or prevent diseases in living organisms.

• Concanavalin A: A type of lectin obtained from jack beans that binds to glucose and mannose residues.

• Ricin: A highly toxic protein derived from castor beans, inhibiting protein synthesis in cells.

Lead Question – 2024 (Jhajjar)

Match List-I with List-II

List-I | List-II

A. Toxin | I. Gum

B. Polymeric substance | II. Concanavalin A

C. Lectin | III. Ricin

D. Drug | IV. Vinblastin

1. A-III, B-IV, C-II, D-I

2. A-II, B-IV, C-I, D-III

3. A-III, B-I, C-II, D-IV

4. A-II, B-I, C-IV, D-III

Explanation: The correct answer is 3. A-III, B-I, C-II, D-IV. Toxin (Ricin) is a poisonous protein, polymeric substances like gums are plant exudates, Concanavalin A is a lectin that binds carbohydrates, and Vinblastin is a drug used in cancer therapy. Each substance plays a distinct role in biological and medicinal processes.

1. Which of the following is a protein that binds to carbohydrates and is used in cell recognition studies?

1. Ricin

2. Concanavalin A

3. Cellulose

4. Histone

Explanation: Concanavalin A is a lectin that specifically binds to glucose and mannose residues. It is widely used in biochemistry to study glycoproteins and cell surface carbohydrates. Lectins like Concanavalin A play a significant role in immune recognition, plant defense, and cell adhesion processes.

2. Which plant produces the toxin Ricin?

1. Abrus precatorius

2. Ricinus communis

3. Catharanthus roseus

4. Glycine max

Explanation: Ricin is a deadly protein toxin extracted from the seeds of Ricinus communis (castor plant). It inhibits protein synthesis by inactivating ribosomes, causing severe cellular damage. Even small doses can be fatal. Despite its toxicity, the castor plant has industrial uses for oil extraction.

3. Vinblastin, a chemotherapeutic drug, is extracted from which plant?

1. Catharanthus roseus

2. Digitalis purpurea

3. Papaver somniferum

4. Atropa belladonna

Explanation: The anticancer drug Vinblastin is obtained from Catharanthus roseus (Madagascar periwinkle). It inhibits cell division by preventing spindle formation during mitosis. Vinblastin and vincristine are vital alkaloids used in treating cancers like leukemia and Hodgkin’s lymphoma. Their discovery revolutionized plant-based chemotherapy.

4. Which of the following pairs is correctly matched?

1. Morphine – Antibiotic

2. Quinine – Antimalarial

3. Ricin – Hormone

4. Concanavalin A – Lipid

Explanation: The correct pair is Quinine – Antimalarial. Quinine is a natural alkaloid extracted from the bark of the Cinchona tree. It interferes with parasite metabolism and is effective against malaria-causing Plasmodium species. Quinine was one of the first plant-derived drugs used in medical history.

5. Which of the following polymeric substances is secreted by plants for protection and wound healing?

1. Gum

2. Latex

3. Resin

4. Alkaloid

Explanation: Gum is a polymeric substance secreted by plants in response to injury. It consists mainly of polysaccharides and helps seal wounds and prevent microbial invasion. Examples include gum arabic and gum tragacanth. These are also commercially valuable as stabilizers and emulsifiers in industries.

6. Which among the following is an example of an alkaloid?

1. Quinine

2. Gum arabic

3. Pectin

4. Concanavalin A

Explanation: Quinine is an alkaloid derived from the bark of Cinchona trees. Alkaloids are nitrogen-containing organic compounds with pharmacological effects. They often serve as defense molecules in plants and are widely used as drugs, stimulants, and poisons. Examples include morphine, nicotine, and caffeine.

7. Assertion-Reason Type:

Assertion (A): Vinblastin inhibits cell division by interfering with spindle fiber formation.

Reason (R): Vinblastin stabilizes microtubules during mitosis.

1. Both A and R are true, and R is the correct explanation of A.

2. Both A and R are true, but R is not the correct explanation of A.

3. A is true, but R is false.

4. Both A and R are false.

Explanation: The correct answer is 3. A is true, but R is false. Vinblastin prevents polymerization of microtubules, thereby blocking spindle formation and arresting mitosis. It does not stabilize microtubules; rather, it depolymerizes them, leading to cell cycle arrest during metaphase. This property makes it effective in cancer treatment.

8. Matching Type:

Match the plant product with its chemical nature:

A. Morphine | I. Alkaloid

B. Gum arabic | II. Polysaccharide

C. Ricin | III. Protein

D. Anthocyanin | IV. Pigment

1. A-I, B-II, C-III, D-IV

2. A-II, B-I, C-IV, D-III

3. A-III, B-I, C-II, D-IV

4. A-IV, B-III, C-I, D-II

Explanation: The correct match is 1. A-I, B-II, C-III, D-IV. Morphine is an alkaloid, gum arabic is a polysaccharide, ricin is a protein, and anthocyanins are pigments responsible for colors in flowers and fruits. Each compound represents a distinct biochemical class found in plant tissues.

9. Fill in the Blanks:

The toxic protein extracted from castor seeds is known as ________.

1. Concanavalin A

2. Ricin

3. Vinblastin

4. Pectin

Explanation: The correct answer is Ricin. It is a ribosome-inactivating protein that blocks protein synthesis in animal cells. Even minute doses can be lethal. Despite its toxicity, Ricinus communis (castor plant) is cultivated for castor oil, which is widely used in industry and medicine.

10. Choose the Correct Statements:

Statement I: Lectins are proteins that bind to specific sugars on cell surfaces.

Statement II: Ricin is an example of a lectin that is non-toxic.

1. Both statements are correct.

2. Only Statement I is correct.

3. Only Statement II is correct.

4. Both statements are incorrect.

Explanation: The correct answer is 2. Only Statement I is correct. Lectins are sugar-binding proteins that play roles in cell signaling and defense. Ricin, however, is a toxic lectin that inhibits protein synthesis. Therefore, while Statement I is true, Statement II is false due to Ricin’s high toxicity.

Topic: Carbohydrate Metabolism; Subtopic: Glycolysis

Keyword Definitions:

• Glycolysis: The breakdown of glucose into pyruvate releasing energy.

• Phosphorylation: Addition of a phosphate group to a molecule.

• Isomerisation: Conversion of one molecule into another with the same formula but different structure.

• ATP: Adenosine triphosphate, the energy currency of the cell.

• Enzyme: A biological catalyst that speeds up biochemical reactions.

• Substrate-level phosphorylation: Direct synthesis of ATP from ADP during metabolism.

Lead Question – 2024 (Jhajjar)

In glycolysis, the conversion of 1,3-bisphosphoglyceric acid to 3-phosphoglyceric acid is:

1. Energy yielding process

2. Energy utilising process

3. Phosphorylation process

4. Isomerisation process

Explanation: The conversion of 1,3-bisphosphoglyceric acid to 3-phosphoglyceric acid is an energy-yielding process catalyzed by the enzyme phosphoglycerate kinase. During this step, ATP is synthesized from ADP through substrate-level phosphorylation. It represents one of the two ATP-generating reactions in glycolysis, producing energy directly within the cytoplasm.

1. Which enzyme catalyzes the first phosphorylation reaction in glycolysis?

1. Hexokinase

2. Phosphofructokinase

3. Aldolase

4. Enolase

Explanation: The first phosphorylation in glycolysis is catalyzed by hexokinase, which converts glucose into glucose-6-phosphate using one ATP molecule. This irreversible reaction traps glucose inside the cell, committing it to the glycolytic pathway. It ensures that glucose remains available for subsequent energy-yielding steps in metabolism.

2. The enzyme enolase catalyzes the conversion of:

1. 2-phosphoglycerate to phosphoenolpyruvate

2. 3-phosphoglycerate to 2-phosphoglycerate

3. Fructose-1,6-bisphosphate to glyceraldehyde-3-phosphate

4. Glucose to glucose-6-phosphate

Explanation: Enolase catalyzes the dehydration of 2-phosphoglycerate to phosphoenolpyruvate (PEP). This step introduces a high-energy enol phosphate bond, preparing the substrate for ATP generation. It’s a crucial preparatory step before pyruvate formation and energy release in the final stages of glycolysis.

3. Which of the following steps in glycolysis involves oxidation?

1. Glyceraldehyde-3-phosphate → 1,3-bisphosphoglycerate

2. Glucose → Glucose-6-phosphate

3. Fructose-6-phosphate → Fructose-1,6-bisphosphate

4. Phosphoenolpyruvate → Pyruvate

Explanation: The oxidation step in glycolysis occurs when glyceraldehyde-3-phosphate is converted to 1,3-bisphosphoglycerate. This reaction, catalyzed by glyceraldehyde-3-phosphate dehydrogenase, involves the reduction of NAD⁺ to NADH. It is the only oxidative step in glycolysis and contributes to the cell’s reducing power.

4. The net gain of ATP molecules per molecule of glucose during glycolysis is:

1. 2

2. 4

3. 6

4. 8

Explanation: The net gain of ATP per molecule of glucose during glycolysis is 2. Four ATP molecules are produced through substrate-level phosphorylation, but two are consumed during the preparatory phase. Therefore, the overall energy yield is 2 ATP and 2 NADH per glucose molecule, under anaerobic conditions.

5. Which of the following is not an intermediate of glycolysis?

1. Pyruvate

2. Citrate

3. Fructose-1,6-bisphosphate

4. Phosphoenolpyruvate

Explanation: Citrate is not an intermediate of glycolysis; it belongs to the citric acid cycle. Glycolysis intermediates include glucose-6-phosphate, 3-phosphoglycerate, and phosphoenolpyruvate. Citrate forms when acetyl-CoA combines with oxaloacetate in the Krebs cycle, representing aerobic energy metabolism.

6. The enzyme catalyzing the last step of glycolysis is:

1. Pyruvate kinase

2. Hexokinase

3. Aldolase

4. Phosphofructokinase

Explanation: Pyruvate kinase catalyzes the final step of glycolysis, converting phosphoenolpyruvate (PEP) to pyruvate. This reaction produces one molecule of ATP via substrate-level phosphorylation. It is an irreversible and highly regulated step, ensuring efficient energy extraction from glucose breakdown.

7. Assertion-Reason Type:

Assertion (A): Glycolysis occurs in the cytoplasm of the cell.

Reason (R): Enzymes of glycolysis are located in mitochondria.

1. Both A and R are true, and R is the correct explanation of A.

2. Both A and R are true, but R is not the correct explanation of A.

3. A is true, but R is false.

4. A is false, but R is true.

Explanation: The correct answer is 3. A is true, but R is false. Glycolysis occurs entirely in the cytoplasm, where all enzymes involved in the pathway are present. Mitochondria are involved in aerobic respiration, not glycolysis. Therefore, the assertion is correct while the reason is false.

8. Matching Type:

Match List I with List II

List I – Enzyme | List II – Reaction

A. Hexokinase | I. Glucose → Glucose-6-phosphate

B. Enolase | II. 2-Phosphoglycerate → PEP

C. Aldolase | III. F-1,6-bisphosphate → DHAP + G3P

D. Pyruvate kinase | IV. PEP → Pyruvate

1. A-I, B-II, C-III, D-IV

2. A-II, B-I, C-IV, D-III

3. A-III, B-IV, C-I, D-II

4. A-IV, B-III, C-II, D-I

Explanation: The correct answer is 1. A-I, B-II, C-III, D-IV. Each enzyme in glycolysis catalyzes a specific substrate conversion. Hexokinase initiates glucose phosphorylation, enolase dehydrates 2-phosphoglycerate, aldolase splits F-1,6-bisphosphate, and pyruvate kinase generates ATP in the final step of glycolysis.

9. Fill in the Blanks:

In glycolysis, the enzyme that converts phosphoenolpyruvate to pyruvate is ________.

1. Pyruvate kinase

2. Enolase

3. Phosphoglycerate kinase

4. Hexokinase

Explanation: The enzyme responsible for converting phosphoenolpyruvate to pyruvate is pyruvate kinase. It catalyzes the substrate-level phosphorylation of ADP to ATP. This step marks the end of glycolysis, producing two molecules of pyruvate per glucose molecule and contributing to cellular energy production.

10. Choose the Correct Statements:

Statement I: ATP is consumed in the initial stages of glycolysis.

Statement II: ATP is generated in later stages of glycolysis.

1. Both statements are correct.

2. Only Statement I is correct.

3. Only Statement II is correct.

4. Both statements are incorrect.

Explanation: The correct answer is 1. Both statements are correct. During glycolysis, ATP is used in the phosphorylation of glucose and fructose-6-phosphate, while ATP is generated during the conversion of 1,3-bisphosphoglycerate and phosphoenolpyruvate to their respective products. The balance ensures a net gain of 2 ATP molecules. 

Topic: Polysaccharides; Subtopic: Complex Polysaccharides

Keyword Definitions:

• Polysaccharides: Large carbohydrate molecules formed by the condensation of many monosaccharides.

• Complex Polysaccharides: Structural or storage polysaccharides with branching or diverse monomer composition.

• Inulin: A polymer of fructose units found in tubers, used for carbohydrate storage.

• Chitin: A nitrogen-containing polysaccharide forming the exoskeleton of arthropods.

• Glucosamine: A monosaccharide derivative forming structural polymers like chitin.

• N-acetyl galactosamine: An amino sugar found in glycoproteins and glycolipids.

Lead Question - 2024 (Jhajjhar)
Which of the following is not a complex polysaccharide?
1. Inulin
2. Chitin
3. Glucosamine
4. N-acetyl galactosamine

Explanation: Glucosamine is not a complex polysaccharide; it is a monosaccharide derivative containing an amino group. Inulin and chitin are polymeric carbohydrates with structural and storage functions, while N-acetyl galactosamine is an amino sugar unit in glycoproteins. Hence, Glucosamine is not a complex polysaccharide. (Answer: 3)

1. Which of the following polysaccharides serves as a major structural component in fungi cell walls?
1. Cellulose
2. Chitin
3. Glycogen
4. Starch
Explanation: The fungal cell wall is composed of chitin, a polymer of N-acetylglucosamine, providing rigidity and strength. It resembles cellulose structurally but contains nitrogen, differentiating it from plant polysaccharides. Hence, Chitin is the correct answer. (Answer: 2)

2. Which polysaccharide is stored in the liver and muscles of animals?
1. Glycogen
2. Cellulose
3. Starch
4. Amylose
Explanation: Glycogen is the storage polysaccharide in animals, made of glucose monomers with α-1,4 and α-1,6 linkages. It serves as a readily mobilizable energy reserve in liver and muscle tissues. Hence, the correct answer is Glycogen. (Answer: 1)

3. Inulin is mainly found in which plant organ?
1. Seeds
2. Tubers
3. Leaves
4. Stems
Explanation: Inulin is a fructose polymer found mainly in the tubers of plants like dahlia and chicory. It serves as a carbohydrate reserve and is soluble in water, unlike starch. Hence, Tubers is the correct answer. (Answer: 2)

4. Which of the following polysaccharides is a homopolysaccharide?
1. Starch
2. Chitin
3. Hyaluronic acid
4. Peptidoglycan
Explanation: Homopolysaccharides are composed of only one type of monosaccharide. Starch is made entirely of glucose units and functions as a storage polysaccharide in plants. Chitin, though polymeric, is a nitrogen derivative; hence Starch fits the definition. (Answer: 1)

5. Cellulose and chitin differ in the presence of which group?
1. Hydroxyl group
2. Amino group
3. Carbonyl group
4. Carboxyl group
Explanation: Cellulose is composed of β-D-glucose units, while chitin has N-acetylglucosamine monomers, containing an amino group (-NH₂). This nitrogen substitution gives rigidity to chitin, distinguishing it from cellulose. Hence, Amino group is correct. (Answer: 2)

6. Which of the following is a heteropolysaccharide?
1. Amylose
2. Glycogen
3. Hyaluronic acid
4. Starch
Explanation: Hyaluronic acid is a heteropolysaccharide containing alternating N-acetylglucosamine and glucuronic acid units. It forms part of connective tissues and synovial fluid, giving lubrication and elasticity. Thus, Hyaluronic acid is the correct answer. (Answer: 3)

7. Assertion-Reason Type:
Assertion (A): Starch is a mixture of amylose and amylopectin.
Reason (R): Amylose is a branched polymer while amylopectin is linear.
1. Both A and R are true and R explains A.
2. Both A and R are true but R does not explain A.
3. A is true but R is false.
4. A is false but R is true.
Explanation: Starch indeed contains amylose and amylopectin. However, amylose is unbranched (linear), and amylopectin is branched. Hence, the assertion is true but the reason is false. Correct answer: 3.

8. Matching Type:
Match the following:
A. Glycogen — (i) Animals
B. Cellulose — (ii) Plants
C. Chitin — (iii) Fungi
D. Inulin — (iv) Tubers
1. A-(i), B-(ii), C-(iii), D-(iv)
2. A-(ii), B-(i), C-(iii), D-(iv)
3. A-(i), B-(iii), C-(ii), D-(iv)
4. A-(iv), B-(ii), C-(i), D-(iii)
Explanation: Glycogen stores energy in animals, cellulose in plant walls, chitin in fungi exoskeletons, and inulin in tubers. Thus, the correct match is 1.

9. Fill in the Blanks:
The structural polysaccharide present in arthropod exoskeletons is __________.
1. Cellulose
2. Chitin
3. Pectin
4. Glycogen
Explanation: Chitin, composed of N-acetylglucosamine monomers, provides rigidity and protection to arthropod exoskeletons and fungal cell walls. Hence, the correct answer is Chitin. (Answer: 2)

10. Choose the Correct Statements (Statement I & II):
Statement I: Cellulose is digestible by humans.
Statement II: Cellulose has β-1,4 linkages between glucose units.
1. Both statements are true.
2. Both statements are false.
3. Statement I true, Statement II false.
4. Statement I false, Statement II true.
Explanation: Humans lack cellulase enzyme to hydrolyze β-1,4 linkages in cellulose, making it indigestible. Statement I is false, but Statement II is true. Hence, correct answer is 4.

Topic: Amino Acids and Proteins; Subtopic: Zwitter Ion Nature of Amino Acids

Keyword Definitions:
• Zwitter Ion: A molecule carrying both positive and negative charges but electrically neutral overall.
• Amino Acid: Organic compound containing both amino (-NH₂) and carboxyl (-COOH) groups.
• pH: The hydrogen ion concentration determining acidity or alkalinity of a solution.
• Isoelectric Point: The pH at which an amino acid exists predominantly as a zwitter ion.
• Functional Groups: Reactive parts of molecules that determine their chemical behavior.

Lead Question – 2024 (Jhajjhar)
The following can be found as a zwitter ion:
1. Fatty acid
2. Monosaccharide
3. Amino acid
4. Nucleic acid
Explanation: Amino acids can exist as zwitter ions due to the presence of both acidic (-COOH) and basic (-NH₂) groups. At physiological pH, the carboxyl group donates a proton forming COO⁻, while the amino group accepts a proton forming NH₃⁺. This dual charge keeps the molecule electrically neutral yet internally charged, stabilizing its structure. Answer: Amino acid.

1. Which of the following amino acids is neutral at physiological pH?
1. Lysine
2. Glutamic acid
3. Glycine
4. Arginine
Explanation: Glycine is a neutral amino acid because its side chain is a single hydrogen atom, making it non-polar and uncharged at physiological pH. It still exists as a zwitter ion, carrying both positive and negative charges that balance each other. Answer: Glycine.

2. The isoelectric point of an amino acid is the pH at which:
1. It acts as a strong acid
2. It acts as a strong base
3. It exists as a zwitter ion
4. It ionizes completely
Explanation: The isoelectric point (pI) of an amino acid is the pH at which the molecule carries no net electric charge, existing predominantly as a zwitter ion. At this point, the positive and negative charges balance perfectly, leading to minimal solubility in water. Answer: It exists as a zwitter ion.

3. Which group in an amino acid donates a proton to form the zwitter ion?
1. -NH₂ group
2. -COOH group
3. -OH group
4. -CH₃ group
Explanation: The carboxyl (-COOH) group donates a proton (H⁺) to the amino (-NH₂) group within the same molecule, forming COO⁻ and NH₃⁺. This internal proton transfer results in a zwitter ion, which is stable at physiological pH. Answer: -COOH group.

4. Fill in the Blank:
At physiological pH, an amino acid exists predominantly as a ____________.
1. Cation
2. Anion
3. Zwitter ion
4. Neutral molecule
Explanation: At physiological pH (~7.4), amino acids exist as zwitter ions because their carboxyl group is deprotonated (-COO⁻) and their amino group is protonated (-NH₃⁺). This dual charge keeps the molecule overall neutral yet charged internally. Answer: Zwitter ion.

5. Which of the following statements is correct regarding a zwitter ion?
1. It has equal positive and negative charges.
2. It is an ionic compound.
3. It is insoluble in water.
4. It carries a net positive charge.
Explanation: A zwitter ion has equal positive and negative charges, maintaining overall electrical neutrality. The internal ionic nature enhances solubility in water. Hence, amino acids as zwitter ions remain stable and reactive in aqueous biological environments. Answer: It has equal positive and negative charges.

6. Choose the correct statements:
Statement I: Zwitter ions are amphoteric.
Statement II: They act only as acids.
1. Both statements are true
2. Both statements are false
3. Statement I true, Statement II false
4. Statement I false, Statement II true
Explanation: Zwitter ions are amphoteric because they can act as both acids (donate protons) and bases (accept protons). Thus, they help maintain pH balance in biological systems. Answer: Statement I true, Statement II false.

7. Assertion-Reason:
Assertion (A): Amino acids exist as zwitter ions in solution.
Reason (R): Because they contain both acidic and basic groups in the same molecule.
1. Both A and R are true and R is the correct explanation of A
2. Both A and R are true but R is not the correct explanation
3. A is true but R is false
4. A is false but R is true
Explanation: Both assertion and reason are true, and the reason correctly explains the assertion. The coexistence of acidic (-COOH) and basic (-NH₂) groups enables internal proton transfer, forming a zwitter ion. Answer: Option 1.

8. Matching Type:
Match the amino acid with its characteristic.
A. Glycine → I. Simplest amino acid
B. Alanine → II. Contains methyl side chain
C. Lysine → III. Basic amino acid
D. Glutamic acid → IV. Acidic amino acid
1. A-I, B-II, C-III, D-IV
2. A-II, B-I, C-IV, D-III
3. A-III, B-IV, C-I, D-II
4. A-IV, B-III, C-II, D-I
Explanation: Glycine is the simplest amino acid. Alanine has a methyl side chain. Lysine is basic, while Glutamic acid is acidic due to its carboxyl side chain. Answer: A-I, B-II, C-III, D-IV.

9. Which of the following amino acids has a polar side chain?
1. Serine
2. Valine
3. Leucine
4. Alanine
Explanation: Serine possesses a hydroxyl (-OH) group in its side chain, making it polar and capable of hydrogen bonding. This property enhances solubility and interaction within proteins. Answer: Serine.

10. The zwitter ionic form of an amino acid contains:
1. -NH₂ and -COOH groups
2. -NH₃⁺ and -COOH groups
3. -NH₂ and -COO⁻ groups
4. -NH₃⁺ and -COO⁻ groups
Explanation: In its zwitter ion form, the amino group becomes protonated (-NH₃⁺) and the carboxyl group becomes deprotonated (-COO⁻). These opposite charges balance internally, creating an overall neutral but dipolar molecule. Answer: -NH₃⁺ and -COO⁻ groups.

Topic: Enzymes; Subtopic: Properties and Nature of Enzymes

Keyword Definitions:

• Enzymes: Biological catalysts that speed up biochemical reactions in living organisms.

• Substrate Specificity: The property of an enzyme to act only on a specific substrate.

• Thermophilic Organisms: Microorganisms that thrive at high temperatures, often above 60°C.

• Metal Ions: Cofactors such as Zn²⁺, Mg²⁺, or Fe²⁺ that assist enzyme function.

Lead Question – 2024 (Jhajjhar)

Which of the following statement is incorrect about enzymes?

(1) They are highly substrate specific
(2) In thermophilic organisms enzymes can catalyze reactions at high temperatures i.e. 90°C
(3) All enzymes are proteinaceous in nature
(4) Some enzymes have metal ions

Explanation: The incorrect statement is (3). Not all enzymes are purely proteinaceous; some, like ribozymes, are RNA molecules that act as catalysts. Enzymes show substrate specificity, and thermophilic enzymes can function at high temperatures. Metal ions often act as cofactors to enhance enzyme activity. Hence, ribozymes are exceptions to protein-only enzymes.

1. Which enzyme converts glucose to glucose-6-phosphate during glycolysis?
(1) Hexokinase
(2) Phosphofructokinase
(3) Aldolase
(4) Pyruvate kinase

Explanation: The correct answer is (1). Hexokinase catalyzes the phosphorylation of glucose to form glucose-6-phosphate, the first step in glycolysis. This reaction requires ATP and ensures that glucose remains inside the cell. The enzyme’s high affinity for glucose makes it crucial in maintaining blood sugar levels under normal conditions.

2. Which of the following is a non-protein enzyme?
(1) Catalase
(2) Pepsin
(3) Ribozyme
(4) Urease

Explanation: The correct answer is (3). Ribozymes are RNA molecules that catalyze specific biochemical reactions, similar to protein enzymes. They are found in ribosomes where they assist in peptide bond formation during protein synthesis. This discovery proved that not all enzymes are made of proteins, expanding our understanding of catalysis.

3. Which factor does NOT affect enzyme activity?
(1) Temperature
(2) pH
(3) Light intensity
(4) Substrate concentration

Explanation: The correct answer is (3). Enzyme activity is influenced by temperature, pH, and substrate concentration but not by light intensity. Enzymes are biological catalysts that function best at optimal pH and temperature, while deviations can denature the enzyme and reduce its catalytic efficiency.

4. Enzymes increase the rate of a chemical reaction by:
(1) Increasing activation energy
(2) Decreasing activation energy
(3) Increasing the substrate concentration
(4) Changing equilibrium

Explanation: The correct answer is (2). Enzymes work by lowering the activation energy required for a reaction to occur, thus speeding up the rate without being consumed in the process. They do not alter the equilibrium of the reaction but enable it to reach equilibrium faster through efficient catalysis.

5. Coenzymes are generally derived from:
(1) Proteins
(2) Vitamins
(3) Minerals
(4) Lipids

Explanation: The correct answer is (2). Coenzymes are organic molecules derived mainly from vitamins, such as NAD⁺ from niacin and FAD from riboflavin. They assist enzymes in catalyzing reactions by carrying chemical groups or electrons between molecules, thus playing a vital role in metabolism.

6. The enzyme that hydrolyses starch into maltose is:
(1) Lipase
(2) Maltase
(3) Amylase
(4) Sucrase

Explanation: The correct answer is (3). Amylase breaks down starch into maltose units, aiding in carbohydrate digestion. It is present in saliva (salivary amylase) and pancreatic juice (pancreatic amylase). This enzymatic action ensures the conversion of complex polysaccharides into absorbable sugars during digestion.

7. (Assertion-Reason Type)
Assertion (A): Enzymes act as biological catalysts.
Reason (R): Enzymes increase activation energy to speed up reactions.
(1) Both A and R are true, and R is the correct explanation of A
(2) Both A and R are true, but R is not the correct explanation of A
(3) A is true, but R is false
(4) A is false, but R is true

Explanation: The correct answer is (3). Enzymes indeed act as biological catalysts, but they lower—not increase—the activation energy. This reduction allows reactions to proceed more rapidly under physiological conditions, enabling life-sustaining biochemical processes in living organisms.

8. (Matching Type)
Match List I with List II:
List I - Enzyme
A. Lipase
B. Pepsin
C. Amylase
D. Urease

List II - Substrate
I. Protein
II. Fat
III. Starch
IV. Urea

(1) A-II, B-I, C-III, D-IV
(2) A-I, B-II, C-IV, D-III
(3) A-IV, B-III, C-I, D-II
(4) A-II, B-III, C-I, D-IV

Explanation: The correct answer is (1). Lipase acts on fats, pepsin on proteins, amylase on starch, and urease on urea. Each enzyme is specific to its substrate due to the complementary structure of the active site, maintaining the principle of enzyme specificity in biological systems.

9. (Fill in the Blank)
The enzyme that converts hydrogen peroxide (H₂O₂) into water and oxygen is ________.
(1) Catalase
(2) Oxidase
(3) Peroxidase
(4) Dehydrogenase

Explanation: The correct answer is (1). Catalase decomposes hydrogen peroxide into water and oxygen, preventing oxidative damage to cells. This enzyme is found in peroxisomes and protects living tissues from toxic effects of accumulated H₂O₂, ensuring cellular metabolic balance.

10. (Choose the Correct Statements)
Statement I: Enzymes are denatured at high temperatures.
Statement II: Enzymes change the equilibrium position of reactions.
(1) Both statements are true
(2) Both statements are false
(3) Statement I is true but Statement II is false
(4) Statement I is false but Statement II is true

Explanation: The correct answer is (3). Enzymes are sensitive to temperature; high heat denatures them, destroying their catalytic properties. However, enzymes do not change the equilibrium of a reaction—they only accelerate the rate at which equilibrium is achieved by lowering activation energy.

Topic: Enzymes; Subtopic: Mechanism of Enzyme Action

Keyword Definitions:
• Enzyme: Biological catalyst that speeds up biochemical reactions without being consumed.
• Active Site: Region of enzyme where substrate molecules bind and undergo chemical reaction.
• Substrate: Reactant molecule on which an enzyme acts.
• Enzyme-Substrate Complex: Temporary intermediate formed when enzyme binds to its substrate.
• Product: Molecule formed after enzyme catalysis.

Lead Question - 2024
Regarding catalytic cycle of an enzyme action, select the correct sequential steps:
A. Substrate enzyme complex formation.
B. Free enzyme ready to bind with another substrate.
C. Release of products.
D. Chemical bonds of the substrate broken.
E. Substrate binding to active site.

(1) A,E,B,D,C
(2) B,A,C,D,E
(3) E,D,C,B,A
(4) E,A,D,C,B

Answer: (4) E,A,D,C,B

Explanation: Enzyme action follows a specific catalytic sequence. The substrate first binds to the active site (E), forming an enzyme-substrate complex (A). The substrate’s chemical bonds are then broken or rearranged (D), resulting in the release of products (C). Finally, the enzyme becomes free (B) to bind with another substrate, repeating the cycle efficiently.

1. Which of the following models best explains enzyme-substrate interaction?
(1) Lock and Key Model
(2) Fluid Mosaic Model
(3) Zwitterion Model
(4) Endosymbiotic Model

Answer: (1) Lock and Key Model

Explanation: The Lock and Key Model explains enzyme specificity, where the substrate fits precisely into the enzyme’s active site like a key into a lock. This structural complementarity ensures that only specific substrates undergo catalysis, providing high precision and efficiency in metabolic processes within living cells.

2. The induced-fit model of enzyme action suggests that:
(1) Enzyme shape remains fixed during catalysis.
(2) Substrate shape changes to fit enzyme.
(3) Enzyme adjusts its shape to fit substrate.
(4) No structural change occurs in enzyme or substrate.

Answer: (3) Enzyme adjusts its shape to fit substrate.

Explanation: The induced-fit model proposed by Daniel Koshland states that enzymes are flexible structures. When a substrate binds, the enzyme undergoes conformational changes to form an optimal fit. This dynamic adjustment lowers activation energy, enhances specificity, and facilitates catalytic reactions vital for metabolism and cellular energy regulation.

3. Which part of enzyme catalysis is directly responsible for lowering activation energy?
(1) Product release
(2) Enzyme-substrate complex formation
(3) Substrate diffusion
(4) Enzyme denaturation

Answer: (2) Enzyme-substrate complex formation

Explanation: The enzyme-substrate complex stabilizes the transition state of the reaction, reducing activation energy. This allows reactants to convert into products faster under mild biological conditions. The enzyme’s specific orientation and microenvironment promote bond rearrangements, ensuring rapid catalysis and maintaining energy efficiency within biological systems.

4. Which of the following factors does not affect enzyme activity?
(1) Temperature
(2) pH
(3) Enzyme concentration
(4) Colour of substrate

Answer: (4) Colour of substrate

Explanation: Enzyme activity is influenced by factors such as temperature, pH, substrate concentration, and enzyme concentration. These parameters affect molecular collisions and enzyme structure. However, the substrate’s colour has no biochemical significance in determining enzyme efficiency or catalytic rate, since enzyme specificity depends on molecular structure, not visual appearance.

5. Enzyme activity doubles with every 10°C rise in temperature until a limit is reached. Beyond that, activity declines due to:
(1) Enzyme activation
(2) Substrate denaturation
(3) Enzyme denaturation
(4) Increased viscosity

Answer: (3) Enzyme denaturation

Explanation: Enzymes are protein molecules sensitive to heat. A moderate rise in temperature increases molecular movement, enhancing enzyme activity. However, excessive heat disrupts hydrogen and ionic bonds in the enzyme’s structure, leading to denaturation and loss of catalytic function. This irreversible process alters the active site, stopping substrate binding.

6. Which of the following enzymes catalyzes the conversion of starch to maltose?
(1) Maltase
(2) Amylase
(3) Lipase
(4) Sucrase

Answer: (2) Amylase

Explanation: Amylase catalyzes the hydrolysis of starch into maltose by breaking α-1,4-glycosidic bonds. It is secreted in saliva and pancreatic juice, initiating carbohydrate digestion. This enzyme functions best around neutral pH and optimum temperature, ensuring effective starch breakdown into simpler sugars for energy production during metabolism.

Assertion-Reason Type Question
7. Assertion (A): Enzymes speed up biochemical reactions.
Reason (R): Enzymes provide energy to start the reaction.
(1) Both A and R are true, and R is the correct explanation of A.
(2) Both A and R are true, but R is not the correct explanation of A.
(3) A is true, but R is false.
(4) A is false, but R is true.

Answer: (3) A is true, but R is false.

Explanation: Enzymes accelerate reactions not by providing energy but by lowering the activation energy required. They create a favorable environment for bond breaking and formation, thereby speeding up reaction rates. The reactants’ intrinsic energy remains unchanged; only the pathway to product formation becomes energetically efficient.

Matching Type Question
8. Match the enzymes with their respective substrates:
A. Lipase  1. Proteins
B. Amylase 2. Lipids
C. Pepsin  3. Starch
(1) A-1, B-2, C-3
(2) A-2, B-3, C-1
(3) A-3, B-2, C-1
(4) A-2, B-1, C-3

Answer: (2) A-2, B-3, C-1

Explanation: Lipase acts on lipids to yield fatty acids and glycerol (A-2). Amylase hydrolyzes starch into maltose and glucose (B-3). Pepsin, a gastric enzyme, breaks down proteins into smaller peptides (C-1). These enzyme-substrate relationships ensure proper digestion of macronutrients essential for growth and metabolic activities.

Fill in the Blanks Type Question
9. The non-protein part of an enzyme essential for its activity is called ________.
(1) Apoenzyme
(2) Cofactor
(3) Substrate
(4) Product

Answer: (2) Cofactor

Explanation: Many enzymes require a non-protein component called a cofactor, which may be a metal ion or an organic coenzyme. It helps in stabilizing the enzyme’s structure or directly participates in the catalytic process. Without cofactors, certain enzymes remain inactive, forming an apoenzyme-cofactor complex called a holoenzyme for activity.

Choose the Correct Statements Type Question
10. Statement I: Enzyme activity is influenced by pH and temperature.
Statement II: Denaturation of enzyme increases its catalytic efficiency.
(1) Both statements are true.
(2) Both statements are false.
(3) Statement I is true, Statement II is false.
(4) Statement I is false, Statement II is true.

Answer: (3) Statement I is true, Statement II is false.

Explanation: Enzymes are highly sensitive to pH and temperature, which affect their structure and activity. Optimum conditions allow maximum reaction rates, while deviations cause denaturation and loss of catalytic function. Denaturation alters the enzyme’s active site, preventing substrate binding and reducing, not enhancing, catalytic efficiency.

Topic: Enzymes; Subtopic: Specificity of Enzymes and Types of Bonds Hydrolyzed

Keyword Definitions:

• Enzyme: A biological catalyst that speeds up chemical reactions in living organisms without being consumed.

• Lipase: An enzyme that hydrolyzes ester bonds in fats into glycerol and fatty acids.

• Nuclease: An enzyme that cleaves phosphodiester bonds in nucleic acids.

• Protease: An enzyme that breaks peptide bonds in proteins and polypeptides.

• Amylase: An enzyme that hydrolyzes glycosidic bonds in starch to release sugars.

• Bond types: Ester, peptide, glycosidic, and phosphodiester bonds are key linkages in biomolecules.

Lead Question – 2024
Match List I with List II
A. Lipase – I. Peptide bond
B. Nuclease – II. Ester bond
C. Protease – III. Glycosidic bond
D. Amylase – IV. Phosphodiester bond
Choose the correct answer from the options given below:
(1) A-III, B-II, C-I, D-IV
(2) A-II, B-IV, C-I, D-III
(3) A-IV, B-I, C-III, D-II
(4) A-IV, B-II, C-III, D-I

Explanation: Lipase hydrolyzes ester bonds in fats, Nuclease breaks phosphodiester bonds in nucleic acids, Protease cleaves peptide bonds in proteins, and Amylase hydrolyzes glycosidic bonds in polysaccharides. Hence, the correct matching is (2) A-II, B-IV, C-I, D-III. Each enzyme exhibits substrate specificity and catalyzes only one type of biochemical bond, ensuring efficient metabolic regulation.

Guessed Questions:

1. Which of the following enzymes acts on lipids?
(1) Amylase
(2) Lipase
(3) Protease
(4) Nuclease
Explanation: Lipase catalyzes the hydrolysis of ester bonds in triglycerides, releasing fatty acids and glycerol. It is secreted by the pancreas and plays a vital role in fat digestion. The enzyme acts specifically on lipid molecules, maintaining energy balance. Hence, the correct answer is (2) Lipase, which acts on dietary fats and oils efficiently.

2. Which enzyme hydrolyzes nucleic acids into nucleotides?
(1) Protease
(2) Nuclease
(3) Lipase
(4) Amylase
Explanation: Nucleases break down nucleic acids such as DNA and RNA by hydrolyzing phosphodiester bonds between nucleotides. This enzyme is crucial during digestion and DNA repair mechanisms. It ensures recycling of nucleotides for cellular functions. Therefore, the correct answer is (2) Nuclease, which specifically cleaves phosphodiester linkages within or between nucleic acid chains.

3. Proteases are responsible for breaking which type of bonds?
(1) Peptide bonds
(2) Ester bonds
(3) Glycosidic bonds
(4) Phosphodiester bonds
Explanation: Proteases catalyze the hydrolysis of peptide bonds between amino acids in proteins. These enzymes are essential for protein digestion and turnover in cells. Pepsin, trypsin, and chymotrypsin are major proteases in humans. Hence, the correct answer is (1) Peptide bonds, which link amino acids and are broken by proteolytic enzymes during digestion.

4. Which of the following enzymes converts starch into maltose?
(1) Amylase
(2) Lipase
(3) Nuclease
(4) Protease
Explanation: Amylase breaks α-1,4-glycosidic bonds in starch, producing maltose and dextrins. It is secreted by salivary glands and the pancreas. This enzyme initiates carbohydrate digestion in the mouth and continues in the small intestine. Hence, the correct answer is (1) Amylase, a carbohydrate-hydrolyzing enzyme crucial for polysaccharide breakdown.

5. Which of the following is a characteristic feature of enzymes?
(1) They are used up during reaction
(2) They increase activation energy
(3) They are highly specific
(4) They act on all substrates
Explanation: Enzymes are biocatalysts that are highly specific, acting only on particular substrates due to their unique active site configuration. They lower activation energy and are not consumed during reactions. Hence, the correct answer is (3) They are highly specific, ensuring selective and efficient biochemical reactions within cells and organisms.

6. Which enzyme class is responsible for breaking bonds by adding water molecules?
(1) Hydrolases
(2) Oxidoreductases
(3) Ligases
(4) Transferases
Explanation: Hydrolases catalyze hydrolysis reactions, adding water to break covalent bonds in biomolecules. Examples include proteases, lipases, and nucleases. These enzymes function in digestion and metabolic degradation. Therefore, the correct answer is (1) Hydrolases, which mediate cleavage of macromolecules such as proteins, nucleic acids, and lipids by hydrolytic action.

7. Assertion–Reason Type:
Assertion (A): Enzymes are highly specific in their action.
Reason (R): Each enzyme can catalyze multiple unrelated reactions.
(1) Both A and R are true, and R is the correct explanation of A
(2) Both A and R are true, but R is not the correct explanation of A
(3) A is true but R is false
(4) A is false but R is true
Explanation: Enzymes possess unique active sites that bind to specific substrates only. Hence, they are highly specific, and each catalyzes a particular reaction. The reason is false because enzymes cannot catalyze multiple unrelated reactions. Therefore, the correct answer is (3) A is true but R is false, highlighting enzyme selectivity in metabolism.

. Matching Type:
Match List I with List II
A. Protease – I. Peptide bond
B. Lipase – II. Ester bond
C. Nuclease – III. Phosphodiester bond
D. Amylase – IV. Glycosidic bond
(1) A-I, B-II, C-III, D-IV
(2) A-II, B-I, C-IV, D-III
(3) A-IV, B-III, C-I, D-II
(4) A-III, B-IV, C-II, D-I
Explanation: Protease hydrolyzes peptide bonds in proteins, Lipase acts on ester bonds in fats, Nuclease breaks phosphodiester bonds in nucleic acids, and Amylase acts on glycosidic linkages in carbohydrates. Hence, the correct matching is (1) A-I, B-II, C-III, D-IV, representing the functional classification of hydrolytic enzymes in biological systems.

9. Fill in the Blanks:
________ catalyzes the breakdown of proteins into peptides and amino acids.
(1) Lipase
(2) Protease
(3) Nuclease
(4) Amylase
Explanation: Protease enzymes degrade proteins by hydrolyzing peptide bonds, producing smaller peptides and amino acids. They are essential for digestion and cellular protein recycling. Proteolytic enzymes like trypsin and pepsin perform these reactions efficiently. Hence, the correct answer is (2) Protease, which catalyzes the breakdown of complex proteins into absorbable amino acid units.

10. Choose the Correct Statements:
Statement I: Lipase hydrolyzes glycosidic bonds in starch.
Statement II: Nuclease hydrolyzes phosphodiester bonds in nucleic acids.
(1) Both I and II are true
(2) Both I and II are false
(3) I is true but II is false
(4) I is false but II is true
Explanation: Lipase acts on ester bonds in lipids, not glycosidic bonds, while nucleases break phosphodiester bonds linking nucleotides in DNA and RNA. Hence, Statement I is false and Statement II is true. Therefore, the correct answer is (4) I is false but II is true, accurately describing enzymatic bond specificity.

Topic: Enzymes and Proteins; Subtopic: Functional Biomolecules and Their Roles

Keyword Definitions:

• GLUT–1: A glucose transporter protein that enables facilitated diffusion of glucose into cells.

• Insulin: A peptide hormone secreted by the β-cells of the pancreas that regulates blood glucose levels.

• Trypsin: A proteolytic enzyme that hydrolyzes peptide bonds in proteins during digestion.

• Collagen: A structural protein that forms the main component of connective tissues like tendons and skin.

Lead Question – 2024

Match List I with List II
List I                                List II
A. GLUT–1                               I. Hormone
B. Insulin                                  II. Enzyme
C. Trypsin                                  III. Intercellular ground substance
D. Collagen                               IV. Enables glucose transport into cells

Choose the correct answer from the options given below:
(1) A–I, B–II, C–III, D–IV
(2) A–II, B–III, C–IV, D–I
(3) A–III, B–IV, C–I, D–II
(4) A–IV, B–I, C–II, D–III

Explanation: GLUT–1 facilitates glucose entry into cells, Insulin is a peptide hormone that lowers blood sugar levels, Trypsin is a digestive enzyme secreted as trypsinogen, and Collagen is a structural connective tissue protein. Hence, the correct match is A–IV, B–I, C–II, D–III. This classification reflects key biomolecular functions essential for metabolism and structure. Correct answer: (4).

1. Which of the following enzymes helps in digestion of proteins in the small intestine?
(1) Amylase
(2) Trypsin
(3) Lipase
(4) Maltase
Explanation: Trypsin, secreted by the pancreas in its inactive form (trypsinogen), helps in hydrolyzing peptide bonds in proteins, producing smaller peptides and amino acids. It acts in the duodenum under alkaline conditions and complements pepsin’s function in protein digestion. Hence, the correct answer is (2).

2. Which of the following is a structural protein?
(1) Collagen
(2) Amylase
(3) Insulin
(4) Pepsin
Explanation: Collagen is the most abundant structural protein found in connective tissues, providing tensile strength to tendons, ligaments, and skin. It forms triple-helical fibers and is critical in maintaining tissue integrity. Unlike enzymes, collagen does not catalyze reactions. Correct answer: (1).

3. Which transport mechanism involves GLUT–1?
(1) Active transport
(2) Facilitated diffusion
(3) Osmosis
(4) Endocytosis
Explanation: GLUT–1 mediates facilitated diffusion, enabling glucose transport across the plasma membrane without energy expenditure. It ensures steady glucose uptake in tissues like the brain and red blood cells. This process depends on concentration gradients, not ATP. Correct answer: (2).

4. Which organ secretes Insulin?
(1) Liver
(2) Pancreas
(3) Kidney
(4) Adrenal gland
Explanation: Insulin is secreted by β-cells of the Islets of Langerhans in the pancreas. It promotes glucose uptake by cells and glycogen synthesis, thus lowering blood glucose levels. Deficiency leads to diabetes mellitus. Correct answer: (2).

5. Which amino acid is abundant in collagen?
(1) Tryptophan
(2) Glycine
(3) Methionine
(4) Tyrosine
Explanation: Collagen is rich in Glycine, Proline, and Hydroxyproline, which enable tight triple-helix formation. Glycine, being the smallest amino acid, fits efficiently in the structure, providing stability and strength to connective tissues. Correct answer: (2).

6. Which enzyme activates Trypsinogen into Trypsin?
(1) Pepsin
(2) Enterokinase
(3) Amylase
(4) Lipase
Explanation: Trypsinogen is converted to active Trypsin by Enterokinase (Enteropeptidase) in the small intestine. This activation initiates a cascade of digestive enzyme activations aiding protein digestion. Correct answer: (2).

7. Assertion (A): Insulin facilitates glucose uptake in cells.
Reason (R): GLUT–1 is a transporter that helps glucose enter cells.
(1) Both A and R are true, and R is the correct explanation of A.
(2) Both A and R are true, but R is not the correct explanation of A.
(3) A is true, but R is false.
(4) A is false, but R is true.
Explanation: Both statements are true but not directly explanatory. Insulin increases glucose uptake by inducing GLUT–4 in muscle and adipose tissues, while GLUT–1 is insulin-independent. Correct answer: (2).

8. Match the following:
A. Pepsin    I. Stomach
B. Trypsin   II. Small intestine
C. Amylase   III. Mouth
D. Lipase     IV. Pancreas
(1) A–I, B–II, C–III, D–IV
(2) A–III, B–I, C–II, D–IV
(3) A–I, B–IV, C–II, D–III
(4) A–II, B–I, C–III, D–IV
Explanation: Pepsin acts in the stomach, Trypsin in the small intestine (secreted by the pancreas), Amylase begins starch digestion in the mouth, and Lipase acts in the pancreas and intestines. Correct answer: (1).

9. Fill in the blanks: Collagen is a __________ protein found abundantly in __________ tissues.
(1) Fibrous, connective
(2) Globular, muscular
(3) Hormonal, epithelial
(4) Structural, nervous
Explanation: Collagen is a fibrous structural protein present in connective tissues like tendons, ligaments, and cartilage. It provides elasticity and tensile strength. Correct answer: (1).

10. Statement I: Insulin acts as a hormone for regulating blood sugar.
Statement II: GLUT–1 acts as an enzyme to digest glucose.
(1) Both statements are true.
(2) Statement I is true, Statement II is false.
(3) Both statements are false.
(4) Statement I is false, Statement II is true.
Explanation: Insulin is a hormone that lowers blood sugar, while GLUT–1 is a transporter protein, not an enzyme. It aids glucose transport but does not digest it. Hence, only Statement I is correct. Correct answer: (2).

Topic: Enzyme Kinetics; Subtopic: Enzyme Inhibition

Keyword Definitions:

• Enzyme: A protein that catalyzes biochemical reactions.

• Substrate: A molecule upon which an enzyme acts.

• Inhibitor: A substance that decreases enzyme activity.

• Competitive inhibition: Inhibition where inhibitor resembles substrate and binds to enzyme's active site.

• Feedback inhibition: End product inhibits an earlier step in the pathway.

• Succinic dehydrogenase: An enzyme of the TCA cycle catalyzing conversion of succinate to fumarate.

• Malonate: A competitive inhibitor structurally similar to succinate.

Lead Question – 2024

Inhibition of Succinic dehydrogenase enzyme by malonate is a classical example of:

(1) Feedback inhibition
(2) Competitive inhibition
(3) Enzyme activation
(4) Cofactor inhibition

Explanation: Malonate inhibits succinic dehydrogenase by competing with succinate for the enzyme's active site. It does not affect other enzymes or steps in the pathway, and inhibition is reversible. This is a textbook example of competitive inhibition because the inhibitor resembles the substrate structurally and prevents substrate binding. Feedback inhibition involves end-product regulation, which is different. Enzyme activation and cofactor inhibition are unrelated mechanisms. Competitive inhibitors increase the apparent Km without changing Vmax, demonstrating classical enzyme kinetics. (Answer: 2)

1. Single Correct Answer:
Which of the following will increase the rate of a competitively inhibited enzyme reaction?
(1) Increase substrate concentration
(2) Increase inhibitor concentration
(3) Decrease enzyme concentration
(4) Decrease pH

Explanation: In competitive inhibition, the inhibitor competes with substrate for the active site. Increasing substrate concentration can outcompete the inhibitor, restoring enzyme activity. Increasing inhibitor or decreasing enzyme reduces activity, and pH changes can denature enzymes but are not specific to overcoming inhibition. Hence, adding more substrate overcomes competitive inhibition. (Answer: 1)

2. Single Correct Answer:
In competitive inhibition, which of the following kinetic changes is observed?
(1) Vmax decreases, Km unchanged
(2) Km increases, Vmax unchanged
(3) Both Vmax and Km decrease
(4) Both Vmax and Km increase

Explanation: Competitive inhibitors increase the apparent Km because more substrate is needed to reach half-maximal velocity, while Vmax remains unchanged as the inhibition can be overcome by high substrate concentration. Non-competitive inhibition reduces Vmax without affecting Km. This classic kinetic signature distinguishes competitive inhibition. (Answer: 2)

3. Single Correct Answer:
Malonate is structurally similar to which substrate in the TCA cycle?
(1) Fumarate
(2) Oxaloacetate
(3) Succinate
(4) Citrate

Explanation: Malonate resembles succinate structurally and competes for succinic dehydrogenase's active site. By occupying the binding site, it prevents succinate conversion to fumarate. This illustrates substrate mimicry in competitive inhibition. It does not resemble fumarate, oxaloacetate, or citrate. (Answer: 3)

4. Single Correct Answer:
Which type of inhibition is reversible and can be overcome by excess substrate?
(1) Non-competitive inhibition
(2) Competitive inhibition
(3) Feedback inhibition
(4) Irreversible inhibition

Explanation: Competitive inhibition is reversible and substrate-dependent. Excess substrate competes with the inhibitor for the active site, restoring enzyme activity. Non-competitive and irreversible inhibition cannot be overcome by substrate increase. Feedback inhibition regulates pathways but is not necessarily reversible by substrate. (Answer: 2)

5. Single Correct Answer:
Which statement about succinic dehydrogenase is correct?
(1) Catalyzes conversion of succinate to fumarate
(2) Requires ATP as cofactor
(3) Located in cytosol
(4) Irreversibly inhibited by malonate

Explanation: Succinic dehydrogenase is a mitochondrial enzyme of the TCA cycle, catalyzing succinate to fumarate conversion. It uses FAD as cofactor, is located in the inner mitochondrial membrane, and is reversibly inhibited by malonate. ATP is not a cofactor, and inhibition is competitive and reversible. (Answer: 1)

6. Single Correct Answer:
Which factor does NOT affect competitive inhibition?
(1) Substrate concentration
(2) Inhibitor concentration
(3) Temperature within optimal range
(4) Enzyme concentration

Explanation: Competitive inhibition is influenced by substrate and inhibitor concentrations. Within optimal temperature range, enzyme activity is stable; temperature changes affect activity but not the competitive mechanism directly. Enzyme concentration affects reaction rate but not inhibition type. Therefore, temperature within optimal limits does not directly affect competitive inhibition. (Answer: 3)

7. Assertion-Reason:
Assertion (A): Malonate is a competitive inhibitor of succinic dehydrogenase.
Reason (R): It binds irreversibly to the active site of the enzyme.
(1) Both A and R are true, R explains A
(2) Both A and R are true, R does not explain A
(3) A true, R false
(4) A false, R true

Explanation: Malonate is indeed a competitive inhibitor, but it binds reversibly to the active site, not irreversibly. Competitive inhibition is reversible and can be overcome by increasing substrate concentration. Therefore, assertion is true, reason is false. (Answer: 3)

8. Matching Type:
Match Enzyme with Inhibitor Type:
A. Succinic dehydrogenase – (i) Competitive
B. Hexokinase – (ii) Feedback inhibition
C. Acetylcholinesterase – (iii) Irreversible inhibition
Options:
(1) A-i, B-ii, C-iii
(2) A-ii, B-i, C-iii
(3) A-i, B-iii, C-ii
(4) A-iii, B-ii, C-i

Explanation: Succinic dehydrogenase is competitively inhibited by malonate. Hexokinase is regulated via feedback inhibition by glucose-6-phosphate. Acetylcholinesterase inhibitors can be irreversible, binding covalently to the enzyme. Matching accurately reflects these classical enzyme inhibition examples. (Answer: 1)

9. Fill in the Blanks:
Malonate binds to the ___ of succinic dehydrogenase, preventing ___ from binding.
(1) Active site, substrate
(2) Allosteric site, cofactor
(3) Regulatory site, product
(4) Substrate site, coenzyme

Explanation: Malonate competes with succinate for the active site of succinic dehydrogenase. By occupying the active site, it prevents substrate binding. This is the hallmark of competitive inhibition, differentiating it from allosteric or feedback inhibition mechanisms. (Answer: 1)

10. Choose Correct Statements:
Statement I: Competitive inhibitors resemble the substrate structurally.
Statement II: Competitive inhibition increases Km but does not change Vmax.
Options:
(1) Both statements are true
(2) Statement I true, Statement II false
(3) Statement I false, Statement II true
(4) Both statements are false

Explanation: Competitive inhibitors are substrate analogs that bind the active site, increasing apparent Km as more substrate is needed to achieve half-maximal velocity. Vmax remains unchanged because high substrate concentrations can overcome the inhibition. Both statements correctly describe competitive inhibition. (Answer: 1)

Topic: Enzyme Cofactors; Subtopic: Metal Ion Cofactors

Keyword Definitions:

• Enzyme: Biological catalysts that speed up chemical reactions without being consumed.

• Cofactor: Non-protein chemical compound required for the biological activity of some enzymes.

• Carboxypeptidase: Proteolytic enzyme that cleaves amino acids from the carboxyl end of proteins or peptides.

• Niacin: Water-soluble vitamin B3 involved in NAD/NADP coenzymes.

• Flavin: Component of FAD/FMN, acting as a redox cofactor in enzymes.

• Haem: Iron-containing porphyrin group, cofactor for hemoproteins and some enzymes.

• Zinc: Metal ion cofactor required for the catalytic activity of some enzymes, including carboxypeptidase.

• Metal Ion Cofactor: A metal ion essential for the structural stability or catalytic function of enzymes.

• Proteolytic Enzyme: Enzymes that hydrolyze peptide bonds in proteins.

• Active Site: Specific region of an enzyme where substrate molecules bind and undergo a chemical reaction.

• Hydrolysis: Chemical reaction involving the breaking of a bond using water.

Lead Question - 2024:

The cofactor of the enzyme carboxypeptidase is:
(1) Niacin
(2) Flavin
(3) Haem
(4) Zinc

Explanation: Correct answer is (4) Zinc. Carboxypeptidase is a zinc-dependent protease enzyme that hydrolyzes the carboxyl-terminal amino acid from proteins and peptides. Zinc acts as a cofactor by stabilizing the enzyme-substrate complex and activating a water molecule for nucleophilic attack on the peptide bond. Niacin, flavin, and haem are cofactors for other enzymes, not carboxypeptidase. Zinc’s presence in the active site is critical for catalytic function, and deficiency in zinc impairs proteolytic activity. This illustrates the importance of metal ion cofactors in enzymatic reactions and structural stability of enzymes, particularly in hydrolysis reactions.

Guessed MCQs:

1. Single Correct Answer MCQ: Which metal ion is essential for the catalytic activity of carboxypeptidase?
(A) Iron
(B) Magnesium
(C) Zinc
(D) Calcium
Explanation: Correct answer is (C). Zinc is required at the active site of carboxypeptidase to stabilize the transition state and assist in peptide bond hydrolysis. Other metals like iron, magnesium, or calcium are not involved in this enzyme's catalysis.

2. Single Correct Answer MCQ: The function of carboxypeptidase is:
(A) Remove amino acids from N-terminal
(B) Remove amino acids from C-terminal
(C) Oxidize substrates
(D) Phosphorylate proteins
Explanation: Correct answer is (B). Carboxypeptidase cleaves amino acids sequentially from the C-terminal end of proteins or peptides, a process facilitated by the zinc cofactor in the active site for hydrolysis.

3. Single Correct Answer MCQ: Which cofactor type does carboxypeptidase require?
(A) Organic cofactor
(B) Metal ion cofactor
(C) Vitamin B derivative
(D) Flavin group
Explanation: Correct answer is (B). Carboxypeptidase requires a metal ion, zinc, as a cofactor. Organic cofactors and vitamin derivatives are involved in other enzyme systems, not in this proteolytic reaction.

4. Single Correct Answer MCQ: Deficiency of which metal impairs carboxypeptidase activity?
(A) Sodium
(B) Iron
(C) Zinc
(D) Potassium
Explanation: Correct answer is (C). Zinc deficiency reduces enzymatic hydrolysis of peptide bonds by carboxypeptidase. Sodium, iron, or potassium do not directly affect its activity.

5. Single Correct Answer MCQ: Niacin acts as a cofactor for:
(A) Carboxypeptidase
(B) Dehydrogenases
(C) Lysozyme
(D) Amylase
Explanation: Correct answer is (B). Niacin is part of NAD/NADP and functions as a coenzyme for dehydrogenases, whereas carboxypeptidase requires zinc.

6. Single Correct Answer MCQ: Haem is a cofactor in:
(A) Carboxypeptidase
(B) Catalase
(C) Amylase
(D) Lipase
Explanation: Correct answer is (B). Haem is the prosthetic group in catalase and peroxidases, facilitating redox reactions. Carboxypeptidase instead uses zinc as its cofactor.

7. Assertion-Reason MCQ:
Assertion (A): Carboxypeptidase requires zinc for activity.
Reason (R): Zinc stabilizes the substrate and activates water for peptide bond hydrolysis.
(A) Both A and R are true and R explains A
(B) Both A and R are true but R does not explain A
(C) A is true, R is false
(D) A is false, R is true
Explanation: Correct answer is (A). Zinc is essential for the catalytic activity of carboxypeptidase. It helps stabilize the substrate in the active site and activates a water molecule for nucleophilic attack, directly explaining the enzyme’s function.

8. Matching Type MCQ: Match enzymes with their cofactors:
List-I: (A) Carboxypeptidase (B) Dehydrogenase (C) Catalase (D) Amylase
List-II: (I) Zinc (II) Niacin (III) Haem (IV) No cofactor
Options:
1. I II III IV
2. II I III IV
3. I III II IV
4. III II I IV
Explanation: Correct answer is 1. Carboxypeptidase uses zinc (I), dehydrogenase uses niacin (II), catalase uses haem (III), and amylase does not require a cofactor (IV).

9. Fill in the Blanks / Completion MCQ: The cofactor of carboxypeptidase is _______.
(A) Niacin
(B) Zinc
(C) Flavin
(D) Haem
Explanation: Correct answer is (B). Zinc is essential for the catalytic function of carboxypeptidase, facilitating hydrolysis of peptide bonds by stabilizing the substrate and activating water molecules.

10. Choose the correct statements MCQ:
Statement I: Zinc acts as a cofactor in carboxypeptidase.
Statement II: Niacin is required for carboxypeptidase activity.
Options:
(A) Both I and II are correct
(B) Only I is correct
(C) Only II is correct
(D) Both are incorrect
Explanation: Correct answer is (B). Zinc is the true cofactor for carboxypeptidase. Niacin is involved in dehydrogenase reactions and is not required for carboxypeptidase activity.

Topic: Lipids; Subtopic: Phospholipids and Lecithin

Keyword Definitions:

• Lecithin: A phospholipid molecule present in cell membranes, aiding structural integrity and signaling.

• Phospholipids: Lipid molecules with glycerol backbone, two fatty acids, and a phosphate group, forming membranes.

• Glycerides: Simple fats composed of glycerol and fatty acids, mainly triglycerides.

• Carbohydrates: Organic compounds of carbon, hydrogen, and oxygen, serving as energy source.

• Amino acids: Building blocks of proteins, containing amino and carboxyl groups.

• Small Molecular Weight Compounds: Molecules with relatively low mass compared to macromolecules.

• Cell Membrane: Lipid bilayer structure enclosing cytoplasm, maintaining homeostasis.

• Hydrophilic Head: Phosphate-containing part of phospholipids that interacts with water.

• Hydrophobic Tail: Fatty acid chains in phospholipids, repelling water and forming bilayers.

• Organic Compounds: Carbon-based molecules essential for life processes.

• Structural Lipids: Lipids contributing to cell membrane stability and function.

Lead Question - 2024:

Lecithin, small molecular weight organic compound found in living tissues, is an example of:
(1) Phospholipids
(2) Glycerides
(3) Carbohydrates
(4) Amino acids

Explanation: Correct answer is (1) Phospholipids. Lecithin is a phospholipid consisting of a glycerol backbone, two fatty acids, and a phosphate group linked to choline. It is amphipathic, having hydrophilic head and hydrophobic tail, which enables formation of cell membranes. It is not a glyceride (triglyceride), carbohydrate, or amino acid. Lecithin also participates in lipid transport, membrane signaling, and emulsification in cells. Its small molecular weight compared to large macromolecules like proteins allows it to integrate efficiently in lipid bilayers. Therefore, it is classified as a key structural phospholipid.

Guessed MCQs:

1. Single Correct Answer MCQ: Lecithin is commonly found in:
(A) Plant and animal cell membranes
(B) Blood plasma only
(C) Muscle fibers only
(D) Nucleic acids
Explanation: Correct answer is (A). Lecithin is abundant in cell membranes of both plants and animals. Its amphipathic nature forms lipid bilayers, providing membrane fluidity, integrity, and selective permeability. It is not exclusive to plasma, muscle, or nucleic acids, but rather integral to membrane structure and cellular function.

2. Single Correct Answer MCQ: The hydrophilic part of lecithin is:
(A) Fatty acid tail
(B) Glycerol backbone
(C) Phosphate-choline head
(D) Carbon chain
Explanation: Correct answer is (C). The phosphate-choline head of lecithin interacts with water, making it hydrophilic. The fatty acid tails are hydrophobic. This amphipathic property allows formation of stable lipid bilayers, critical for cell membrane architecture and biological functions like signaling and transport.

3. Single Correct Answer MCQ: Lecithin aids in:
(A) Protein synthesis
(B) Membrane fluidity
(C) DNA replication
(D) Glycolysis
Explanation: Correct answer is (B). Lecithin, as a phospholipid, contributes to membrane fluidity by maintaining a flexible lipid bilayer. It also aids in vesicle formation, emulsification, and signal transduction. It is not directly involved in protein synthesis, DNA replication, or glycolysis.

4. Single Correct Answer MCQ: Lecithin is classified as:
(A) Triglyceride
(B) Phospholipid
(C) Steroid
(D) Carbohydrate
Explanation: Correct answer is (B). Lecithin is a phospholipid with a glycerol backbone, fatty acid chains, and a phosphate group. Triglycerides lack phosphate groups, steroids have fused rings, and carbohydrates are sugar-based, distinguishing lecithin clearly as a phospholipid.

5. Single Correct Answer MCQ: Lecithin helps in transport of:
(A) Proteins
(B) Lipids
(C) Carbohydrates
(D) Nucleotides
Explanation: Correct answer is (B). Lecithin is key in forming lipoproteins for lipid transport in blood and cellular membranes. Its amphipathic structure allows emulsification of fats. Proteins, carbohydrates, and nucleotides require different transport mechanisms.

6. Single Correct Answer MCQ: The major functional role of lecithin in cells is:
(A) Energy storage
(B) Structural support in membranes
(C) Enzymatic activity
(D) Hormone signaling
Explanation: Correct answer is (B). Lecithin forms structural components of membranes, maintaining bilayer integrity and fluidity. While it participates indirectly in signaling, its primary role is structural, not energy storage or enzymatic activity.

7. Assertion-Reason MCQ:
Assertion (A): Lecithin is essential for membrane formation.
Reason (R): Lecithin is amphipathic with hydrophilic head and hydrophobic tail.
(A) Both A and R are true and R explains A
(B) Both A and R are true but R does not explain A
(C) A is true, R is false
(D) A is false, R is true
Explanation: Correct answer is (A). Lecithin’s amphipathic nature allows it to form stable lipid bilayers, providing membrane structure and selective permeability. Hydrophilic heads face aqueous environments while hydrophobic tails form interior, directly explaining its essential role in membranes.

8. Matching Type MCQ: Match components of lecithin:
List-I: (A) Glycerol backbone (B) Fatty acids (C) Phosphate-choline (D) Hydrophilic head
List-II: (I) Structural scaffold (II) Hydrophobic tail (III) Polar group (IV) Interacts with water
Options: (A) (B) (C) (D)
1. I II III IV
2. I II IV III
3. II I III IV
4. IV III II I
Explanation: Correct answer is 1. Glycerol forms scaffold (I), fatty acids form hydrophobic tails (II), phosphate-choline is polar group (III), and hydrophilic head interacts with water (IV). This explains amphipathic character and membrane role.

9. Fill in the Blanks / Completion MCQ: Lecithin is a ______, important in membranes.
(A) Carbohydrate
(B) Phospholipid
(C) Protein
(D) Steroid
Explanation: Correct answer is (B). Lecithin is a phospholipid consisting of glycerol, fatty acids, and phosphate group. Its amphipathic structure forms bilayers, ensuring membrane integrity, selective permeability, and fluidity. It is not a carbohydrate, protein, or steroid.

10. Choose the correct statements MCQ:
Statement I: Lecithin has hydrophobic tails.
Statement II: Lecithin forms lipid bilayers in membranes.
(A) Only Statement I is correct
(B) Only Statement II is correct
(C) Both I and II are correct
(D) Neither I nor II is correct
Explanation: Correct answer is (C). Lecithin has fatty acid hydrophobic tails and hydrophilic phosphate-choline heads. This amphipathic structure allows formation of bilayers, providing membrane integrity and functional compartmentalization within cells.

Topic: Classification of Biomolecules; Subtopic: Terpenoids, Fatty Acids, Nucleic Acids, Polysaccharides

Keyword Definitions:

• Terpenoids: Naturally occurring organic chemicals derived from five-carbon isoprene units, often used in medicine and fragrances.

• Unsaturated fatty acid: Fatty acids that contain one or more double bonds between carbon atoms in the hydrocarbon chain.

• Nucleic acid: Biopolymers (DNA, RNA) responsible for storing and transmitting genetic information.

• Polysaccharide: Carbohydrates composed of long chains of monosaccharide units linked by glycosidic bonds.

• Codeine: An alkaloid used as a pain reliever and cough suppressant.

• Diterpenes: Terpenoids composed of four isoprene units, often bioactive.

• Ricin: A toxic protein derived from castor bean.

• Concanavalin A: A lectin protein that binds specific sugar molecules.

• Lectin: Proteins that recognize and bind carbohydrates specifically.

• Alkaloid: Nitrogen-containing organic compound with significant physiological effects.

• Bioactive: Compounds that affect biological systems.

Lead Question - 2023 (Manipur)

Match List - I with List - II

List-I List-II

(A) Terpenoids (I) Codeine

(B) Unsaturated fatty acid (II) Diterpenes

(C) Nucleic acid (III) Ricin

(D) Polysaccharide (IV) Concanavalin A

Choose the correct answer from the options given below:

Options: (A) (B) (C) (D)

1. II IV III I

2. II I IV III

3. II III I IV

4. II IV I III

Explanation:

Terpenoids are derived from isoprene units, and diterpenes specifically consist of four isoprene units, matching option II for (A). Unsaturated fatty acids do not correspond to proteins or lectins, so (B) matches I, Codeine. Nucleic acids, like DNA and RNA, are associated with toxic proteins in experimental context such as Ricin, matching III. Polysaccharides interact with lectins, so (D) corresponds to IV, Concanavalin A. Therefore, the correct match is (A)-(II), (B)-(I), (C)-(III), (D)-(IV), which corresponds to option 2.

1. Single Correct Answer MCQ:

Which of the following is a diterpene?

1. Terpenoids

2. Codeine

3. Linoleic acid

4. Concanavalin A

Explanation:

Diterpenes are a type of terpenoid composed of four isoprene units. Terpenoids include monoterpenes, sesquiterpenes, and diterpenes. Codeine is an alkaloid, linoleic acid is a fatty acid, and Concanavalin A is a protein lectin. Correct answer is 1.

2. Single Correct Answer MCQ:

Ricin is classified as:

1. Protein

2. Polysaccharide

3. Terpenoid

4. Fatty acid

Explanation:

Ricin is a toxic protein derived from castor bean seeds, known for inhibiting protein synthesis. It is not a polysaccharide, terpenoid, or fatty acid. Correct answer is 1.

3. Single Correct Answer MCQ:

Concanavalin A is an example of:

1. Alkaloid

2. Lectin

3. Terpenoid

4. Fatty acid

Explanation:

Concanavalin A is a lectin protein that binds specific carbohydrate residues, often used in biochemical research. It is not an alkaloid, terpenoid, or fatty acid. Correct answer is 2.

4. Single Correct Answer MCQ:

Unsaturated fatty acids are characterized by:

1. Single bonds only

2. Double bonds between carbon atoms

3. Nitrogen atoms in chain

4. Ring structure

Explanation:

Unsaturated fatty acids contain one or more double bonds between carbon atoms, causing kinks in the chain. Saturated fatty acids have single bonds only. Nitrogen atoms or ring structures are not characteristic. Correct answer is 2.

5. Single Correct Answer MCQ:

Codeine is classified as:

1. Terpenoid

2. Alkaloid

3. Protein

4. Polysaccharide

Explanation:

Codeine is a nitrogen-containing alkaloid extracted from opium poppy, used as analgesic and antitussive. It is not a terpenoid, protein, or polysaccharide. Correct answer is 2.

6. Single Correct Answer MCQ:

Which biomolecule stores genetic information?

1. Polysaccharide

2. Nucleic acid

3. Terpenoid

4. Fatty acid

Explanation:

Nucleic acids, DNA and RNA, store and transmit genetic information in cells. Polysaccharides, terpenoids, and fatty acids do not serve this function. Correct answer is 2.

7. Assertion-Reason MCQ:

Assertion (A): Polysaccharides interact with lectins like Concanavalin A.

Reason (R): Lectins are proteins that specifically bind carbohydrates.

1. Both A and R are true and R explains A

2. Both A and R are true but R does not explain A

3. A is true but R is false

4. Both A and R are false

Explanation:

Polysaccharides contain carbohydrate units that can bind lectins. Lectins are proteins with carbohydrate-binding specificity. Therefore, both the assertion and reason are true, and the reason correctly explains the assertion. Correct answer is 1.

8. Matching Type MCQ:

Match the biomolecule with its correct example:

A. Terpenoid — (i) Diterpenes

B. Unsaturated fatty acid — (ii) Linoleic acid

C. Nucleic acid — (iii) DNA

D. Polysaccharide — (iv) Starch

1. A-(i), B-(ii), C-(iii), D-(iv)

2. A-(ii), B-(i), C-(iv), D-(iii)

3. A-(iii), B-(iv), C-(ii), D-(i)

4. A-(iv), B-(iii), C-(i), D-(ii)

Explanation:

Terpenoids include diterpenes, unsaturated fatty acids include linoleic acid, nucleic acids include DNA, and polysaccharides include starch. Correct matching is A-(i), B-(ii), C-(iii), D-(iv), which is option 1.

9. Fill in the Blanks MCQ:

The toxic protein derived from castor bean is called _______.

1. Codeine

2. Ricin

3. Concanavalin A

4. Terpene

Explanation:

Ricin is a highly toxic protein derived from castor bean seeds. Codeine is an alkaloid, Concanavalin A is a lectin, and terpene is a class of natural compounds. Correct answer is 2.

10. Choose the correct statements MCQ:

Statement I: Terpenoids include diterpenes.

Statement II: Concanavalin A is a lectin that binds polysaccharides.

1. Statement I only

2. Statement II only

3. Both statements are true

4. Both statements are false

Explanation:

Terpenoids encompass diterpenes, and Concanavalin A is a lectin that specifically binds to carbohydrate residues in polysaccharides. Both statements are accurate. Correct answer is 3.

Topic: Proteins and Hormones; Subtopic: Structure and Function of Insulin

Keyword Definitions:

• Insulin: A peptide hormone secreted by pancreatic β-cells that regulates glucose metabolism.

• Polypeptide chain: A linear sequence of amino acids linked by peptide bonds forming proteins.

• C-peptide: A connecting peptide linking A and B chains in proinsulin, removed to form active insulin.

• Disulphide bridges: Covalent bonds between sulfur atoms in cysteine residues stabilizing protein structure.

• Prohormone: An inactive precursor of a hormone requiring enzymatic cleavage for activation.

Lead Question - 2023 (Manipur)

Select incorrect statement regarding chemical structure of insulin:

1. Mature insulin molecule consists of three polypeptide chains - A, B and C.
2. Insulin is synthesized as prohormone which contains extra stretch of C-peptide.
3. C-peptide is not present in mature insulin molecule.
4. Polypeptide chains A and B are linked by disulphide bridges.

Explanation: The mature insulin molecule consists of two polypeptide chains (A and B) linked by disulphide bridges. It is synthesized as a prohormone, proinsulin, which includes a C-peptide that connects A and B chains. During maturation, C-peptide is cleaved and not present in active insulin. Hence, statement 1 is incorrect. (Answer: 1)

Guessed Questions:

1. Which organ secretes insulin?
1. Liver
2. Pancreas
3. Adrenal gland
4. Thyroid gland

Explanation: Insulin is secreted by the β-cells of the islets of Langerhans in the pancreas. It regulates blood glucose by promoting uptake in cells and converting excess glucose to glycogen. Its deficiency causes hyperglycemia and diabetes mellitus. Hence, the correct answer is pancreas. (Answer: 2)

2. The number of disulphide bridges in human insulin is:
1. One
2. Two
3. Three
4. Four

Explanation: Human insulin consists of two inter-chain disulphide bonds connecting A and B chains and one intra-chain disulphide bond within the A-chain, totaling three disulphide bridges. These bonds provide stability and biological functionality to the hormone. Thus, the correct answer is three. (Answer: 3)

3. The C-peptide of proinsulin helps in:
1. Formation of active insulin molecule
2. Regulating glucose uptake
3. Forming glycogen
4. Stimulating glucagon release

Explanation: C-peptide connects A and B chains of proinsulin, ensuring proper folding and structural alignment for active insulin formation. It is cleaved during insulin maturation and serves as a clinical marker for endogenous insulin secretion levels. The correct answer is formation of active insulin molecule. (Answer: 1)

4. Assertion (A): Insulin is a peptide hormone.
Reason (R): It is made up of amino acids linked by peptide bonds.
1. Both A and R are true, and R explains A.
2. Both A and R are true, but R does not explain A.
3. A is true, R is false.
4. A is false, R is true.

Explanation: Insulin, being composed of two amino acid chains joined by peptide and disulphide bonds, is indeed a peptide hormone. The reason correctly explains the assertion since peptide hormones are amino acid-based. Therefore, both statements are true, and R correctly explains A. (Answer: 1)

5. Match the following:
A. Insulin – i. Increases blood glucose
B. Glucagon – ii. Decreases blood glucose
C. Epinephrine – iii. Mobilizes glucose
1. A–ii, B–i, C–iii
2. A–i, B–ii, C–iii
3. A–iii, B–ii, C–i
4. A–ii, B–iii, C–i

Explanation: Insulin decreases blood glucose by facilitating glucose uptake. Glucagon increases blood glucose via glycogenolysis, and epinephrine mobilizes glucose during stress. Correct matching: A–ii, B–i, C–iii. Together, they regulate glucose homeostasis in humans. Thus, the correct answer is option 1. (Answer: 1)

6. Insulin mainly acts on:
1. Brain
2. Muscles and liver
3. Lungs
4. Heart

Explanation: Insulin primarily targets liver, muscle, and adipose tissues to promote glucose uptake and storage as glycogen. It also inhibits gluconeogenesis and lipolysis. The brain is insulin-independent for glucose transport. Hence, insulin mainly acts on muscles and liver. (Answer: 2)

7. Fill in the blanks:
Insulin is synthesized in the _______ of the pancreas.
1. Alpha cells
2. Beta cells
3. Delta cells
4. Acinar cells

Explanation: Insulin is synthesized and secreted by β-cells located in the islets of Langerhans of the pancreas. These cells play a key role in glucose homeostasis by releasing insulin in response to elevated blood sugar levels. Hence, the correct answer is beta cells. (Answer: 2)

8. Choose the correct statements:
Statement I: Insulin promotes glycogen breakdown.
Statement II: Insulin facilitates glucose uptake into cells.
1. Both statements are correct.
2. Both statements are incorrect.
3. Statement I is incorrect, Statement II is correct.
4. Statement I is correct, Statement II is incorrect.

Explanation: Insulin facilitates glucose entry into cells, promoting glycogen synthesis, not its breakdown. Glycogen breakdown is stimulated by glucagon. Therefore, Statement I is incorrect while Statement II is correct. Hence, the correct answer is option 3. (Answer: 3)

9. The gene for human insulin was transferred and expressed first in:
1. Yeast
2. E. coli
3. Bacillus subtilis
4. Aspergillus

Explanation: The first recombinant DNA technology-based human insulin, known as Humulin, was produced using Escherichia coli. The human insulin gene was inserted into bacterial plasmid, allowing bacterial cells to synthesize insulin identical to natural form. Hence, the correct answer is E. coli. (Answer: 2)

10. Insulin deficiency leads to which condition?
1. Hypoglycemia
2. Diabetes mellitus
3. Goitre
4. Obesity

Explanation: Insulin deficiency results in impaired glucose utilization, causing elevated blood glucose levels or hyperglycemia, leading to diabetes mellitus. The disorder is characterized by polyuria, polydipsia, and polyphagia. Hence, the correct answer is diabetes mellitus. (Answer: 2)

Subtopic: Secondary Metabolites

Keyword Definitions:

• Secondary Metabolites: Organic compounds produced by plants not directly involved in growth, development, or reproduction but often involved in defense, pigmentation, or signaling.

• Curcumin: A phenolic compound found in turmeric with medicinal properties; a secondary metabolite.

• Morphine: An alkaloid obtained from opium poppy; used as a painkiller; a secondary metabolite.

• Anthocyanin: Water-soluble pigment responsible for red, purple, or blue colors in plants; a secondary metabolite.

• Lecithin: A phospholipid forming part of cell membranes; primary metabolite involved in structural function.

• Primary Metabolites: Compounds essential for growth and development, including sugars, amino acids, nucleotides, and lipids.

• Alkaloids: Nitrogen-containing secondary metabolites with pharmacological activity.

• Phenolics: Aromatic secondary metabolites involved in defense and pigmentation.

Lead Question – 2023 (Manipur)

Which of the following is not a secondary metabolite?
1. Curcumin
2. Morphine
3. Anthocyanin
4. Lecithin

Explanation: Curcumin, Morphine, and Anthocyanins are all secondary metabolites involved in defense, pigmentation, or medicinal properties. Lecithin, however, is a primary metabolite, a phospholipid essential for cell membrane structure and function. Unlike secondary metabolites, lecithin is directly required for growth and metabolism. Therefore, the compound that is not a secondary metabolite among the given options is Lecithin. Correct answer: 4. Lecithin.

1. Single Correct Answer MCQ:
Which of the following is an alkaloid?
1. Curcumin
2. Morphine
3. Anthocyanin
4. Lecithin
Explanation: Morphine is an alkaloid derived from opium poppy and acts as a secondary metabolite with pharmacological properties. Alkaloids are nitrogen-containing secondary metabolites. Correct answer: 2. Morphine.

2. Single Correct Answer MCQ:
Anthocyanins are classified as:
1. Alkaloids
2. Terpenoids
3. Phenolics
4. Lipids
Explanation: Anthocyanins are water-soluble pigments responsible for red, purple, or blue colors in plants and belong to the phenolic class of secondary metabolites. Correct answer: 3. Phenolics.

3. Single Correct Answer MCQ:
Which of the following is a primary metabolite?
1. Morphine
2. Lecithin
3. Curcumin
4. Anthocyanin
Explanation: Lecithin is a primary metabolite; it is a structural phospholipid essential for cell membrane integrity and growth, unlike secondary metabolites which are not essential for primary growth. Correct answer: 2. Lecithin.

4. Single Correct Answer MCQ:
Curcumin is derived from which plant?
1. Opium poppy
2. Turmeric
3. Beetroot
4. Tea
Explanation: Curcumin is a phenolic secondary metabolite extracted from turmeric (Curcuma longa) and is responsible for its yellow color and medicinal properties. Correct answer: 2. Turmeric.

5. Single Correct Answer MCQ:
Which compound acts as a natural pigment in plants?
1. Morphine
2. Lecithin
3. Anthocyanin
4. Curcumin
Explanation: Anthocyanins are pigments giving red, purple, or blue coloration to flowers and fruits, serving as a secondary metabolite with protective functions. Correct answer: 3. Anthocyanin.

6. Single Correct Answer MCQ:
Which metabolite has medicinal properties as a painkiller?
1. Lecithin
2. Curcumin
3. Morphine
4. Anthocyanin
Explanation: Morphine, an alkaloid secondary metabolite, is derived from opium poppy and is used as a potent analgesic in medicine. Correct answer: 3. Morphine.

7. Assertion-Reason MCQ:
Assertion (A): Lecithin is essential for plant cell structure.
Reason (R): Lecithin is a secondary metabolite involved in pigmentation.
1. Both A and R true, R explains A
2. Both A and R true, R does not explain A
3. A true, R false
4. A false, R true
Explanation: Lecithin is essential for cell membranes (primary metabolite). It is not a secondary metabolite and does not contribute to pigmentation. Correct answer: 3. A true, R false.

8. Matching Type MCQ:
Match metabolite with type:
A. Curcumin – (i) Phenolic
B. Morphine – (ii) Alkaloid
C. Anthocyanin – (iii) Pigment
D. Lecithin – (iv) Primary metabolite
1. A–i, B–ii, C–iii, D–iv
2. A–ii, B–i, C–iv, D–iii
3. A–iii, B–iv, C–i, D–ii
4. A–iv, B–iii, C–ii, D–i
Explanation: Curcumin is phenolic, Morphine is alkaloid, Anthocyanin is pigment, Lecithin is a primary metabolite. Correct option: 1.

9. Fill in the Blanks MCQ:
__________ is a secondary metabolite with pharmacological properties, while __________ is a primary metabolite involved in cell membrane structure.
1. Morphine, Lecithin
2. Lecithin, Morphine
3. Curcumin, Anthocyanin
4. Anthocyanin, Curcumin
Explanation: Morphine is a secondary metabolite with analgesic properties. Lecithin is a primary metabolite, essential for membrane structure. Correct answer: 1.

10. Choose the Correct Statements MCQ:
Statement I: Curcumin is a secondary metabolite.
Statement II: Lecithin is a secondary metabolite.
1. Both true
2. Both false
3. I true, II false
4. I false, II true
Explanation: Curcumin is a secondary metabolite involved in defense and medicinal functions. Lecithin is a primary metabolite essential for membranes. Correct answer: 3.

Chapter: Plant Secondary Metabolites; Topic: Chemical Defense Mechanisms in Plants; Subtopic: Cardiac Glycosides and Herbivore Deterrence

• Calotropis: A common weed that secretes a milky latex containing toxic compounds used as chemical defense against herbivores.

• Cardiac glycosides: Toxic secondary metabolites affecting heart muscle function, deterring herbivory.

• Ricin: A potent toxin derived from castor seeds interfering with protein synthesis.

• Quinine: Bitter alkaloid from Cinchona bark used as antimalarial but acts as herbivore deterrent.

• Strychnine: Alkaloid toxin from Strychnos nux-vomica seeds acting on nervous system.

• Secondary metabolites: Compounds produced by plants not for growth but for defense.

• Herbivory: Feeding of animals on plants causing potential damage to vegetation.

• Latex: Milky fluid secreted by plants like Calotropis containing defensive chemicals.

• Defense mechanism: Strategies evolved by plants to resist or deter predators and herbivores.

• Allelochemicals: Biochemicals influencing interactions between organisms, often for defense.

• Toxin: Harmful chemical produced naturally by living organisms for protection or predation.

Lead Question - 2023 (Manipur)

For chemical defense against herbivores, Calotropis has:

• 1. Cardiac glycosides

• 2. Strychnine

• 3. Toxic ricin

• 4. Distasteful quinine

Explanation: Calotropis secretes a milky latex containing cardiac glycosides, toxic chemicals that interfere with the heart’s normal rhythm when ingested by herbivores. This chemical defense discourages grazing and protects the plant. These glycosides act as potent deterrents against most animals. Strychnine, ricin, and quinine are toxic alkaloids found in other plant species but not in Calotropis. Correct answer: 1.

1. Which of the following is an example of a plant chemical defense?

• a) Production of nectar

• b) Production of cardiac glycosides

• c) Rapid leaf fall

• d) Sunlight reflection by leaves

Explanation: Many plants, including Calotropis, produce cardiac glycosides as chemical defenses to deter herbivory. These compounds cause nausea or cardiac arrest when consumed by animals. Nectar and leaf fall are not defense mechanisms, and sunlight reflection aids temperature regulation. Such chemicals are key survival adaptations. Correct answer: b.

2. Ricin, a toxic protein interfering with protein synthesis, is produced by:

• a) Calotropis

• b) Castor plant

• c) Cinchona

• d) Datura

Explanation: Ricin is a highly toxic protein obtained from castor seeds (Ricinus communis). It inactivates ribosomes, blocking protein synthesis, and is a potent biological toxin. Calotropis produces cardiac glycosides, not ricin, while Cinchona produces quinine and Datura produces tropane alkaloids. Correct answer: b.

3. Which plant produces the alkaloid quinine?

• a) Cinchona

• b) Calotropis

• c) Castor

• d) Strychnos

Explanation: Quinine, a bitter alkaloid used as an antimalarial, is derived from the bark of Cinchona trees. It also acts as a deterrent to herbivores due to its bitterness. Calotropis contains cardiac glycosides, castor has ricin, and Strychnos contains strychnine. Correct answer: a.

4. What type of chemical defense does Datura exhibit?

• a) Production of glycosides

• b) Production of tropane alkaloids

• c) Production of flavonoids

• d) Production of saponins

Explanation: Datura species produce tropane alkaloids like atropine, hyoscyamine, and scopolamine, which are neurotoxic compounds acting as chemical defenses against herbivores. These alkaloids deter grazing due to toxicity and bitter taste. Glycosides, flavonoids, and saponins occur in other plants but serve different functions. Correct answer: b.

5. Which of the following statements about cardiac glycosides is true?

• a) They are proteins that denature easily

• b) They are secondary metabolites affecting the nervous system

• c) They are steroidal compounds affecting heart function

• d) They are carbohydrates used for energy storage

Explanation: Cardiac glycosides are steroidal compounds that inhibit sodium-potassium ATPase in heart tissue, causing cardiac toxicity in herbivores. They act as defensive secondary metabolites, not energy storage molecules. Their bitterness and toxicity prevent animals from feeding on such plants. Correct answer: c.

6. Calotropis latex acts as a chemical defense because it:

• a) Attracts herbivores

• b) Produces nectar for pollinators

• c) Contains toxic cardiac glycosides

• d) Helps in water absorption

Explanation: Calotropis latex is rich in cardiac glycosides and proteolytic enzymes that make it highly toxic and bitter to herbivores. These substances cause nausea and heart irregularities in grazing animals, discouraging feeding. The latex plays no role in water uptake or attraction. Correct answer: c.

7. Assertion (A): Calotropis plants are rarely grazed by animals.
Reason (R): They produce toxic cardiac glycosides that act as deterrents.

• a) Both A and R are true, and R explains A

• b) Both A and R are true, but R does not explain A

• c) A is true, R is false

• d) A is false, R is true

Explanation: Animals avoid grazing on Calotropis due to the presence of toxic cardiac glycosides in its latex, which can cause vomiting and heart irregularities. Hence, both assertion and reason are true, and R correctly explains A. This adaptation prevents loss of plant biomass to herbivory. Correct answer: a.

8. Match the plant with its major defensive chemical:

List-I: (A) Calotropis, (B) Castor, (C) Datura, (D) Cinchona
List-II: (I) Ricin, (II) Quinine, (III) Tropane alkaloids, (IV) Cardiac glycosides

• a) A-IV, B-I, C-III, D-II

• b) A-III, B-II, C-IV, D-I

• c) A-II, B-IV, C-I, D-III

• d) A-I, B-II, C-III, D-IV

Explanation: Calotropis produces cardiac glycosides, Castor produces ricin, Datura synthesizes tropane alkaloids, and Cinchona contains quinine. These represent diverse plant defense mechanisms against herbivores and pathogens. Correct answer: a.

9. Fill in the blank: The toxic substance responsible for Calotropis defense is __________.

• a) Quinine

• b) Cardiac glycosides

• c) Ricin

• d) Caffeine

Explanation: Calotropis uses cardiac glycosides for its chemical defense strategy. These glycosides affect the heart muscles and taste bitter, deterring herbivory. Such toxins are stored in milky latex, preventing loss from grazing animals. Quinine, ricin, and caffeine occur in other plants. Correct answer: b.

10. Choose the correct statements:

Statement I: Calotropis produces cardiac glycosides in latex.
Statement II: These compounds make the plant palatable to herbivores.

• a) Both I and II are correct

• b) I is correct, II is incorrect

• c) I is incorrect, II is correct

• d) Both I and II are incorrect

Explanation: Calotropis contains cardiac glycosides that render it toxic and unpalatable to herbivores. These compounds discourage grazing and act as an effective plant defense. Therefore, Statement I is correct and Statement II is incorrect. This adaptation allows survival in environments with heavy herbivore presence. Correct answer: b.

Topic: Carbohydrates; Subtopic: Polysaccharides

• Inulin: A storage polysaccharide composed mainly of fructose units, found in plants like chicory and garlic.

• Fructose: A monosaccharide sugar commonly found in fruits and honey.

• Polysaccharide: A carbohydrate polymer made up of many monosaccharide units.

• Glucose: A six-carbon monosaccharide sugar used as energy source in cells.

• Galactose: A monosaccharide sugar found in milk and dairy products.

• Amino Acids: Building blocks of proteins, not carbohydrates.

• Chicory: A plant rich in inulin used as a dietary fiber.

• Storage Polysaccharide: A carbohydrate stored in plants or animals for energy supply.

• Oligosaccharides: Carbohydrates made of 2–10 monosaccharide units.

• Prebiotic: Compounds like inulin that promote growth of beneficial gut bacteria.

• Dietary Fiber: Plant-derived carbohydrate that resists digestion in the small intestine.

Lead Question - 2023 (Manipur)

Inulin is a polymer of:

• 1. Fructose

• 2. Galactose

• 3. Amino Acids

• 4. Glucose

Explanation: Inulin is a storage polysaccharide composed mainly of fructose units linked by β-(2→1) glycosidic bonds. It is found in plants like chicory, garlic, and onion and acts as a prebiotic dietary fiber. It is not composed of glucose, galactose, or amino acids. Inulin helps regulate blood sugar and promotes gut health by supporting beneficial bacteria. Correct answer: 1.

1. Which of the following is a storage polysaccharide in plants?

• a) Inulin

• b) Cellulose

• c) Chitin

• d) Lactose

Explanation: Inulin is a storage polysaccharide mainly composed of fructose units in plants like chicory and garlic. Cellulose is structural, chitin is structural in fungi and arthropods, and lactose is a disaccharide in milk. Inulin functions as energy storage and prebiotic fiber. Correct answer: a.

2. Fructans are polymers of:

• a) Glucose

• b) Fructose

• c) Galactose

• d) Amino acids

Explanation: Fructans, including inulin and levan, are polysaccharides made of fructose units linked by β-(2→1) or β-(2→6) glycosidic bonds. Glucose, galactose, or amino acids are not the building units of fructans. Fructans are stored in roots and tubers and act as prebiotics. Correct answer: b.

3. Inulin is commonly found in:

• a) Wheat and rice

• b) Garlic and chicory

• c) Milk and cheese

• d) Egg white

Explanation: Inulin is abundant in garlic, chicory, onion, and Jerusalem artichoke. It is absent in cereals like wheat and rice, dairy products, or animal sources. Its fructose polymer structure allows it to act as prebiotic dietary fiber, supporting beneficial gut microbiota. Correct answer: b.

4. Which property is true for inulin?

• a) Highly digestible in small intestine

• b) Acts as dietary fiber

• c) Composed of amino acids

• d) Found in animal tissues

Explanation: Inulin resists digestion in the small intestine and reaches the colon where it acts as dietary fiber and prebiotic. It is composed of fructose, not amino acids, and is present in plants, not animal tissues. Its fiber property helps regulate gut microbiota and glycemic response. Correct answer: b.

5. The type of glycosidic linkage in inulin is:

• a) α-(1→4)

• b) β-(1→4)

• c) β-(2→1)

• d) α-(1→6)

Explanation: Inulin has β-(2→1) glycosidic linkages between fructose units, forming a linear polymer. α-(1→4) linkages are in starch, β-(1→4) in cellulose, α-(1→6) in branched polysaccharides. This structure confers resistance to digestion and prebiotic function. Correct answer: c.

6. Which of the following is a prebiotic?

• a) Inulin

• b) Lactose

• c) Glucose

• d) Fructose

Explanation: Inulin is a prebiotic because it stimulates growth of beneficial gut bacteria like Bifidobacterium. Lactose, glucose, and fructose are simple sugars digested in the small intestine and do not have prebiotic properties. Inulin supports colon health and regulates microbiota composition. Correct answer: a.

7. Assertion (A): Inulin is a polymer of fructose.
Reason (R): Inulin is digestible in the human small intestine.

• a) Both A and R are true, R explains A

• b) Both A and R are true, R does not explain A

• c) A is true, R is false

• d) A is false, R is true

Explanation: Inulin is a fructose polymer (A is true) but resists digestion in the small intestine, acting as dietary fiber and prebiotic. Therefore, Reason is false. Correct answer: c.

8. Match the plant with the polysaccharide it stores:

• 1. Chicory

• 2. Potato

• 3. Milk

• 4. Onion

a) 1-Inulin, 2-Starch, 3-Lactose, 4-Inulin
b) 1-Starch, 2-Lactose, 3-Inulin, 4-Starch
c) 1-Lactose, 2-Starch, 3-Inulin, 4-Glucose
d) 1-Glucose, 2-Inulin, 3-Starch, 4-Lactose

Explanation: Chicory and onion store inulin, potato stores starch, milk stores lactose. This reflects plant and animal carbohydrate storage patterns. Correct answer: a.

9. Fill in the blank: ____________ is a fructose polymer found in plants like chicory and garlic.

• a) Inulin

• b) Starch

• c) Cellulose

• d) Glycogen

Explanation: Inulin is a polymer of fructose found in chicory, garlic, and onion. Starch and glycogen are glucose polymers; cellulose is a structural β-(1→4) glucose polymer. Inulin serves as storage carbohydrate and prebiotic. Correct answer: a.

10. Choose the correct statements:

Statement I: Inulin is a fructose polymer.
Statement II: Inulin is digestible in the human small intestine.

• a) Both I and II are correct

• b) Only I is correct

• c) Only II is correct

• d) Both I and II are incorrect

Explanation: Inulin is indeed a fructose polymer (Statement I correct). It resists digestion in the small intestine and acts as dietary fiber (Statement II incorrect). Therefore, only Statement I is correct. Correct answer: b.

Chapter: Biomolecules; Topic: Structure and Function of Biomolecules; Subtopic: Proteins, Carbohydrates, Lipids, and Nucleic Acids

Keyword Definitions:
• Protein: Large biomolecules composed of amino acids linked by peptide bonds, performing structural, enzymatic, and regulatory functions in cells.
• Unsaturated fatty acid: Fatty acids containing one or more C=C double bonds in the hydrocarbon chain, liquid at room temperature.
• Nucleic acid: Polymers of nucleotides containing a phosphate group, pentose sugar, and nitrogenous base; DNA and RNA are examples.
• Polysaccharide: Carbohydrate polymers of monosaccharides linked by glycosidic bonds; function as energy storage or structural components.
• Peptide bond: Covalent bond linking amino acids in proteins.
• Glycosidic bond: Covalent bond connecting monosaccharides in carbohydrates.
• Phosphodiester bond: Covalent bond linking nucleotides in nucleic acids.
• C=C double bond: Unsaturated bond present in fatty acids.

Lead Question - 2023 (Manipur)
Match List - I with List - II
List-I List-II
(A) Protein (I) C=C double bonds
(B) Unsaturated fatty acid (II) Phosphodiester bond
(C) Nucleic acid (III) Glycosidic bonds
(D) Polysaccharide (IV) Peptide bonds
Choose the correct answer from the options given below:
Options: (A) (B) (C) (D)
1. II I IV III
2. IV III I II
3. IV I II III
4. I IV III II
Answer & Explanation: Option 2. Proteins are polymers of amino acids linked by peptide bonds (IV). Unsaturated fatty acids contain C=C double bonds (I). Nucleic acids have nucleotides joined via phosphodiester bonds (II). Polysaccharides consist of monosaccharides linked by glycosidic bonds (III). Understanding the types of chemical bonds in biomolecules is essential for explaining their structure-function relationship. Proteins serve as enzymes and structural elements, fatty acids provide energy storage and membrane fluidity, nucleic acids store genetic information, and polysaccharides act as energy reserves or structural components.

1. Single Correct Answer MCQ
Which of the following amino acids contains a sulfur atom in its side chain?
Options:
A. Lysine
B. Methionine
C. Valine
D. Leucine
Answer & Explanation: Option B. Methionine is a sulfur-containing amino acid important for initiating protein synthesis and acting as a methyl group donor in various biochemical reactions. Lysine, valine, and leucine do not have sulfur. Methionine’s sulfur atom is crucial for disulfide bond formation and maintaining protein tertiary structure, contributing to protein stability and function in enzymatic reactions and metabolic processes. Proper understanding of sulfur amino acids is important for studying protein chemistry and cellular metabolism.

2. Single Correct Answer MCQ
Which polysaccharide serves primarily as a storage form of glucose in animals?
Options:
A. Starch
B. Cellulose
C. Glycogen
D. Chitin
Answer & Explanation: Option C. Glycogen is the main glucose storage polysaccharide in animals, highly branched, allowing rapid mobilization of glucose. Starch is the plant storage form. Cellulose provides structural support in plant cell walls, and chitin is found in arthropod exoskeletons. Glycogen is synthesized in the liver and muscles, providing energy during fasting or exercise. Its branched structure facilitates quick release of glucose for metabolic needs. Understanding glycogen is critical in physiology and biochemistry to explain energy storage and mobilization mechanisms.

3. Single Correct Answer MCQ
Which vitamin is fat-soluble and acts as an antioxidant in cell membranes?
Options:
A. Vitamin B1
B. Vitamin C
C. Vitamin E
D. Vitamin B12
Answer & Explanation: Option C. Vitamin E is a fat-soluble vitamin that protects polyunsaturated fatty acids in cell membranes from oxidative damage. Vitamin B1 and B12 are water-soluble vitamins involved in enzymatic reactions. Vitamin C is also water-soluble and functions as an antioxidant in aqueous environments. Vitamin E’s antioxidant property helps maintain membrane integrity, preventing lipid peroxidation, and contributing to cellular defense mechanisms. Its presence in the lipid bilayer ensures protection against reactive oxygen species, supporting healthy cell function.

4. Single Correct Answer MCQ
Which nucleobase is present only in RNA but absent in DNA?
Options:
A. Adenine
B. Cytosine
C. Uracil
D. Guanine
Answer & Explanation: Option C. Uracil is unique to RNA, replacing thymine found in DNA. Adenine, cytosine, and guanine are present in both DNA and RNA. Uracil forms base pairs with adenine during transcription. Its presence allows RNA molecules to function as mRNA, tRNA, and rRNA. Understanding this difference is fundamental in molecular biology and genetics for differentiating DNA from RNA, studying transcription processes, and explaining the flow of genetic information from DNA to protein synthesis.

5. Single Correct Answer MCQ
Which bond is primarily responsible for stabilizing the secondary structure of proteins?
Options:
A. Peptide bond
B. Hydrogen bond
C. Ionic bond
D. Disulfide bond
Answer & Explanation: Option B. Hydrogen bonds stabilize α-helix and β-sheet structures in proteins. Peptide bonds link amino acids linearly, disulfide bonds stabilize tertiary structures, and ionic bonds contribute to tertiary and quaternary interactions. Hydrogen bonding provides directional stability to secondary structures, determining protein folding patterns essential for biological function. Proper secondary structure ensures enzymatic activity, structural support, and interaction with other biomolecules. Understanding hydrogen bonding is crucial in protein chemistry, structural biology, and studying protein misfolding diseases.

6. Single Correct Answer MCQ
Which of the following is an essential fatty acid in humans?
Options:
A. Oleic acid
B. Linoleic acid
C. Palmitic acid
D. Stearic acid
Answer & Explanation: Option B. Linoleic acid is an essential polyunsaturated fatty acid required in the diet, as humans cannot synthesize it. Oleic acid is non-essential, palmitic and stearic acids are saturated fatty acids produced endogenously. Linoleic acid is a precursor for arachidonic acid and eicosanoids, crucial for cellular signaling and inflammation. Recognizing essential fatty acids is important for nutrition, biochemistry, and understanding dietary requirements for maintaining cell membrane integrity and physiological functions.

7. Assertion-Reason MCQ
Assertion (A): RNA contains ribose sugar instead of deoxyribose.
Reason (R): RNA is single-stranded and less stable than DNA.
Options:
A. Both A and R are true, R is the correct explanation of A
B. Both A and R are true, R is not the correct explanation of A
C. A is true, R is false
D. A is false, R is true
Answer & Explanation: Option B. RNA contains ribose sugar making it structurally distinct from DNA which has deoxyribose. RNA is typically single-stranded and less stable due to the 2′-OH group, but this is not the reason for the sugar difference. Understanding sugar composition and strand stability is important in molecular biology, as it affects transcription, translation, and RNA molecule lifespan in the cell.

8. Matching Type MCQ
Match the following enzymes with their substrate:
List-I List-II
(A) Amylase (I) Proteins
(B) Lipase (II) Starch
(C) Protease (III) Lipids
(D) Lactase (IV) Lactose
Options:
1. A-II, B-III, C-I, D-IV
2. A-III, B-II, C-IV, D-I
3. A-IV, B-I, C-III, D-II
4. A-I, B-IV, C-II, D-III
Answer & Explanation: Option 1. Amylase acts on starch (II), Lipase hydrolyzes lipids (III), Protease breaks down proteins (I), and Lactase hydrolyzes lactose (IV). Matching enzyme-substrate pairs is essential in understanding digestion and metabolic processes. Enzymes are highly specific catalysts, and knowing their substrates helps in studying physiological reactions, nutritional science, and clinical enzyme deficiency disorders.

9. Fill in the Blanks / Completion MCQ
The monosaccharide that forms the backbone of nucleotides in DNA is _______.
Options:
A. Ribose
B. Deoxyribose
C. Glucose
D. Fructose
Answer & Explanation: Option B. Deoxyribose is the pentose sugar forming the backbone of DNA nucleotides. Ribose is found in RNA. Glucose and fructose are energy-providing monosaccharides. Deoxyribose contributes to DNA structural stability and enables genetic information storage. Recognizing pentose sugars in nucleotides is crucial for understanding DNA/RNA structure, replication, transcription, and their roles in cellular metabolism.

10. Choose the Correct Statements MCQ
Statement I: Saturated fatty acids have no double bonds and are solid at room temperature.
Statement II: Unsaturated fatty acids contain one or more double bonds and are liquid at room temperature.
Options:
A. Both I and II are correct
B. Only I is correct
C. Only II is correct
D. Both I and II are incorrect
Answer & Explanation: Option A. Saturated fatty acids lack double bonds, resulting in straight chains that pack tightly, making them solid at room temperature. Unsaturated fatty acids contain one or more C=C double bonds, causing kinks that prevent tight packing, making them liquid at room temperature. Understanding fatty acid saturation is essential in nutrition, lipid metabolism, and cellular membrane fluidity regulation.

Topic: Proteins and Hemoglobin Structure; Subtopic: Protein Terminology and Quaternary Structure

Lead Question - 2023

Given below are two statements:
Statement I: A protein is imagined as a line, the left end represented by first amino acid (C-terminal) and the right end represented by last amino acid (N-terminal).
Statement II: Adult human haemoglobin consists of 4 subunits (two α-type and two β-type).
In the light of the above statements, choose the correct answer from the options given below:
(1) Statement I is true but Statement II is false
(2) Statement I is false but Statement II is true
(3) Both Statement I and Statement II are true
(4) Both Statement I and Statement II are false

Answer: (2) Statement I is false but Statement II is true. Proteins have their N-terminal at the start (first amino acid) and C-terminal at the end (last amino acid). Adult human hemoglobin is a tetramer composed of two α-globin and two β-globin subunits. Understanding the correct orientation of protein chains is critical in protein biochemistry, enzyme mechanisms, and structural analysis. Misidentifying the terminals can lead to incorrect interpretation of protein sequences and functionality. Hemoglobin's quaternary structure with α2β2 arrangement is essential for cooperative oxygen binding and efficient transport in blood.

Keyword Definitions:

• N-terminal: The start of a protein or polypeptide chain, containing a free amino group.

• C-terminal: The end of a protein or polypeptide chain, containing a free carboxyl group.

• Haemoglobin: Oxygen-carrying tetrameric protein in red blood cells.

• Subunit: Individual polypeptide chain in a multi-chain protein.

• α-globin: Alpha subunit of hemoglobin.

• β-globin: Beta subunit of hemoglobin.

• Quaternary Structure: Arrangement of multiple protein subunits in a multi-subunit complex.