Biochemistry

Topic: Enzyme Action; Subtopic: Catalysis and Activation Energy

Keyword Definitions:

• Enzyme: Biological catalyst that speeds up chemical reactions by lowering activation energy without being consumed.

• Activation Energy: Minimum energy required for a chemical reaction to reach the transition state and form products.

• Transition State: High-energy intermediate state between substrate and product during a chemical reaction.

• Enzyme-Substrate Complex: Temporary association formed when a substrate binds to the active site of an enzyme.

• Catalysis: Process of increasing reaction rate using an enzyme by stabilizing the transition state.

• Substrate: Molecule upon which an enzyme acts.

• Product: Molecule formed as a result of an enzymatic reaction.

• Reaction Mechanism: Stepwise sequence of elementary reactions showing the pathway from substrate to product.

Lead Question - 2022 (Abroad)
In a reaction catalyzed by an enzyme, which of the following statements is correct ?
1. Enzymes decrease the activation energy for formation of transition state.
2. Enzymes make transition from substrate to product more difficult.
3. Enzymes increase the activation energy for formation of transition state.
4. Enzyme-substrate complex formed during a reaction lasts for a very long time.
Explanation: The correct answer is Enzymes decrease the activation energy for formation of transition state. Enzymes accelerate reactions by stabilizing the transition state and lowering the activation energy barrier, enabling substrates to convert to products more easily. They do not increase activation energy or make the reaction more difficult. The enzyme-substrate complex is transient, existing only briefly during catalysis. By stabilizing the transition state, enzymes reduce the energy required for bond rearrangements, thereby increasing reaction rates efficiently without altering the overall free energy change of the reaction, which is critical for biological regulation of metabolic pathways.

1. Single Correct Answer Type:
What is the function of an enzyme in a biochemical reaction?
1. Increase substrate concentration
2. Decrease activation energy
3. Alter product structure
4. Provide energy for reaction
Explanation: The correct answer is Decrease activation energy. Enzymes function as biological catalysts, lowering the energy barrier required for the reaction to proceed, allowing substrates to form products more efficiently. They do not change substrate concentration, alter product structure, or provide energy. Enzymes accelerate reactions without being consumed, stabilizing the transition state and increasing reaction rate while maintaining specificity. This property is essential for metabolic regulation, enabling cells to control reaction kinetics and energy efficiency in biochemical pathways.

2. Single Correct Answer Type:
The enzyme-substrate complex:
1. Is permanent
2. Is a transient intermediate
3. Increases activation energy
4. Does not bind substrate
Explanation: The correct answer is Is a transient intermediate. The enzyme-substrate complex forms temporarily when a substrate binds to an enzyme's active site. It stabilizes the transition state, lowering activation energy and facilitating conversion to product. The complex is short-lived and dissociates after product formation. It does not permanently bind the substrate, increase activation energy, or prevent catalysis. The transient nature ensures enzymes are reusable, allowing multiple catalytic cycles and efficient control of reaction rates in cellular biochemical processes.

3. Single Correct Answer Type:
Transition state in enzyme-catalyzed reactions represents:
1. Stable substrate
2. High-energy intermediate
3. Final product
4. Enzyme denaturation
Explanation: The correct answer is High-energy intermediate. The transition state is a transient, high-energy configuration of substrate molecules during a reaction. Enzymes stabilize this state, lowering activation energy and facilitating conversion to products. It is not a stable substrate, final product, or related to enzyme denaturation. Transition state stabilization is central to catalysis, allowing enzymes to accelerate reactions efficiently, control reaction specificity, and regulate metabolic pathways. Understanding the transition state is crucial for designing inhibitors or drugs targeting enzyme activity.

4. Single Correct Answer Type:
Which factor is directly reduced by enzyme catalysis?
1. Substrate concentration
2. Activation energy
3. Free energy change
4. Reaction equilibrium
Explanation: The correct answer is Activation energy. Enzymes reduce the energy barrier (activation energy) required to reach the transition state, allowing reactions to proceed faster. They do not change substrate concentration, overall free energy change (ΔG), or shift reaction equilibrium. By lowering activation energy, enzymes increase the rate of reactions under physiological conditions, ensuring efficient metabolism. This principle underlies enzymatic catalysis in all biological systems, enabling tightly regulated and energy-efficient biochemical transformations.

5. Single Correct Answer Type:
Which statement about enzyme catalysis is correct?
1. Enzymes are consumed in the reaction
2. Enzymes alter equilibrium of reaction
3. Enzymes stabilize transition state
4. Enzymes increase activation energy
Explanation: The correct answer is Enzymes stabilize transition state. Enzymes bind substrates and stabilize the high-energy transition state, lowering activation energy and facilitating product formation. They are not consumed, do not alter reaction equilibrium, and do not increase activation energy. This property allows enzymes to accelerate reactions efficiently and repeatedly. Transition state stabilization is key to catalysis, dictating substrate specificity and reaction kinetics, and is fundamental for cellular metabolism and regulation of biochemical pathways.

6. Single Correct Answer Type:
During enzymatic reactions, the duration of the enzyme-substrate complex is:
1. Very long
2. Transient
3. Permanent
4. Irreversible
Explanation: The correct answer is Transient. The enzyme-substrate complex exists temporarily, stabilizing the transition state before the substrate converts into product. It dissociates immediately after catalysis, allowing the enzyme to participate in multiple reaction cycles. It is not permanent, very long-lived, or irreversible. The transient nature is essential for enzyme efficiency, reusability, and regulation of reaction rates. This ensures dynamic control of metabolism, preventing accumulation of intermediates and maintaining homeostasis in cellular biochemical pathways.

7. Assertion-Reason Type:
Assertion (A): Enzymes accelerate chemical reactions.
Reason (R): Enzymes lower the activation energy of a reaction.
1. Both A and R are correct, and R is the correct explanation of A
2. Both A and R are correct, but R is not the correct explanation of A
3. A is correct, R is false
4. A is false, R is true
Explanation: The correct answer is Both A and R are correct, and R is the correct explanation of A. Enzymes increase reaction rates by stabilizing the transition state and lowering activation energy. This makes substrate conversion to product faster and more efficient. Without enzymes, reactions may proceed slowly due to high energy barriers. The principle of catalysis ensures that enzymes are reusable, highly specific, and critical for regulating metabolic pathways, maintaining energy efficiency, and supporting life processes in all biological systems.

8. Matching Type:
Match the terms with their correct description:
A. Substrate → (i) High-energy intermediate
B. Enzyme → (ii) Molecule upon which enzyme acts
C. Transition State → (iii) Biological catalyst
D. Product → (iv) Molecule formed after reaction
1. A-(ii), B-(iii), C-(i), D-(iv)
2. A-(i), B-(ii), C-(iii), D-(iv)
3. A-(iv), B-(i), C-(iii), D-(ii)
4. A-(ii), B-(i), C-(iv), D-(iii)
Explanation: Correct answer is A-(ii), B-(iii), C-(i), D-(iv). The substrate is the molecule acted upon, the enzyme is the catalyst, the transition state is the high-energy intermediate stabilized by the enzyme, and the product is the molecule formed. This organization is fundamental to enzyme-catalyzed reactions, ensuring efficient substrate conversion, controlled reaction rates, and proper regulation of metabolic pathways.

9. Fill in the Blanks / Completion Type:
In enzyme-catalyzed reactions, the ________ is stabilized to lower the activation energy.
1. Substrate
2. Transition State
3. Product
4. Enzyme
Explanation: The correct answer is Transition State. Enzymes stabilize the high-energy transition state of a substrate, reducing the activation energy required to form the product. This stabilization accelerates the reaction without altering overall free energy change. Substrate binds the enzyme temporarily, forming the enzyme-substrate complex, and the product is released after the reaction. The transition state is key to catalysis, ensuring efficient, specific, and regulated biochemical reactions in cells.

10. Choose the Correct Statements Type:
Statement I: Enzymes reduce the activation energy required for a reaction.
Statement II: Enzymes alter the equilibrium constant of a reaction.
1. Both I and II are correct
2. I is correct, II is incorrect
3. I is incorrect, II is correct
4. Both I and II are incorrect
Explanation: Correct answer is I is correct, II is incorrect. Enzymes lower the activation energy by stabilizing the transition state, accelerating reactions without being consumed. They do not change the equilibrium constant; the ratio of product to substrate at equilibrium remains unchanged. Enzyme function is kinetic, affecting reaction rate but not thermodynamics. This distinction is fundamental in biochemistry, allowing precise control of metabolic pathways and ensuring cellular reactions proceed efficiently under physiological conditions.

Topic: Bioactive Compounds

Subtopic: Toxins, Lectins, Drugs, and Alkaloids

• Toxin: A poisonous substance produced by living organisms causing harmful effects on other organisms.

• Abrin: A toxic protein present in Abrus precatorius seeds, classified as a toxin.

• Lectins: Proteins that bind specifically to carbohydrates on cell surfaces.

• Concanavalin A: A lectin extracted from jack bean that binds to specific sugars.

• Ricin: A potent toxin derived from Ricinus communis; not classified as a drug.

• Alkaloids: Nitrogen-containing organic compounds with pharmacological effects.

• Codeine: An alkaloid used as an analgesic and cough suppressant drug.

• Bioactive Compounds: Naturally occurring substances that affect biological systems.

• Phytochemicals: Chemical compounds in plants with health effects.

• Protein Toxins: Proteins like abrin and ricin that inhibit cellular functions.

• Drug Classification: Categorization of bioactive molecules based on physiological effect.

Lead Question - 2021

Identify the incorrect pair.

Options:
1. Toxin – Abrin
2. Lectins – Concanavalin A
3. Drugs – Ricin
4. Alkaloids – Codeine

Explanation: Ricin is a potent protein toxin, not a drug. Abrin is correctly classified as a toxin, Concanavalin A is a lectin, and codeine is an alkaloid with drug activity. The incorrect pair is “Drugs – Ricin”. Answer: Drugs – Ricin.

1. Which compound is a protein toxin?
Options:
A. Codeine
B. Ricin
C. Aspirin
D. Morphine

Explanation: Ricin is a toxic protein that inhibits protein synthesis in cells. It is derived from Ricinus communis seeds and classified as a protein toxin. Other options are drugs or alkaloids with different mechanisms. Answer: Ricin.

2. Abrin is classified as:
Options:
A. Alkaloid
B. Lectin
C. Toxin
D. Drug

Explanation: Abrin is a toxic protein present in seeds of Abrus precatorius, causing cell inhibition. It is correctly classified as a toxin and not as an alkaloid or drug. Answer: Toxin.

3. Concanavalin A belongs to:
Options:
A. Alkaloids
B. Lectins
C. Toxins
D. Drugs

Explanation: Concanavalin A is a lectin extracted from jack beans that binds specifically to sugars on cell surfaces. It is not toxic in small doses, nor an alkaloid or drug. Answer: Lectins.

4. Codeine is a type of:
Options:
A. Alkaloid
B. Lectin
C. Toxin
D. Protein

Explanation: Codeine is an alkaloid obtained from opium, used as an analgesic and cough suppressant. It is not a protein or lectin. Answer: Alkaloid.

5. Which of these is not a lectin?
Options:
A. Concanavalin A
B. Phytohemagglutinin
C. Abrin
D. Wheat germ agglutinin

Explanation: Abrin is a protein toxin, not a lectin. Concanavalin A, phytohemagglutinin, and wheat germ agglutinin are lectins that bind specific carbohydrates. Answer: Abrin.

6. Abrin and ricin both share:
Options:
A. Alkaloid structure
B. Toxic protein property
C. Carbohydrate binding
D. Drug activity

Explanation: Both abrin and ricin are toxic proteins that inhibit cellular protein synthesis, making them potent toxins. They are not alkaloids or drugs. Answer: Toxic protein property.

7. Assertion-Reason:
Assertion (A): Ricin is a potent toxin.
Reason (R): Ricin inhibits protein synthesis inside cells.
Options:
A. Both A and R are true, R is correct explanation
B. Both A and R are true, R is not correct explanation
C. A is true, R is false
D. A is false, R is true

Explanation: Ricin is highly toxic because it inhibits ribosomal protein synthesis, leading to cell death. The reason correctly explains the assertion. Answer: Both A and R are true, R is correct explanation.

8. Match the following:
Column I: 1. Abrin 2. Ricin 3. Concanavalin A 4. Codeine
Column II: A. Toxin B. Drug C. Lectin D. Toxin
Options:
A. 1-A, 2-D, 3-C, 4-B
B. 1-C, 2-A, 3-D, 4-B
C. 1-B, 2-C, 3-A, 4-D
D. 1-D, 2-B, 3-A, 4-C

Explanation: Correct matching: Abrin – Toxin (A), Ricin – Toxin (D), Concanavalin A – Lectin (C), Codeine – Drug (B). Answer: 1-A, 2-D, 3-C, 4-B.

9. Fill in the blank: _______ is a lectin extracted from jack beans.
Options:
A. Ricin
B. Abrin
C. Concanavalin A
D. Codeine

Explanation: Concanavalin A is a lectin from jack beans that binds to specific sugars on cell surfaces, facilitating carbohydrate recognition. Answer: Concanavalin A.

10. Choose the correct statements:
1. Ricin is a toxin.
2. Abrin is a lectin.
3. Codeine is an alkaloid drug.
4. Concanavalin A is a lectin.
Options:
A. 1, 3, 4 only
B. 1, 2, 3, 4
C. 1, 4 only
D. 2, 3 only

Explanation: Statements 1, 3, and 4 are correct. Ricin is a toxin, code

Topic: Amino Acids

Subtopic: Classification of Amino Acids

Keyword Definitions:

• Amino Acid – Organic compounds containing amino (-NH2) and carboxyl (-COOH) groups, building blocks of proteins.

• Basic Amino Acid – Amino acids with positively charged side chains at physiological pH, e.g., lysine, arginine, histidine.

• Acidic Amino Acid – Amino acids with negatively charged side chains at physiological pH, e.g., aspartic acid, glutamic acid.

• Hydrophobic Amino Acid – Amino acids with nonpolar side chains, e.g., valine, leucine, isoleucine.

• Aromatic Amino Acid – Amino acids with aromatic ring in side chain, e.g., tyrosine, phenylalanine, tryptophan.

• pH – Measure of hydrogen ion concentration; determines ionization state of amino acid side chains.

Lead Question - 2020

Identify the basic amino acid from the following:
(1) Lysine
(2) Valine
(3) Tyrosine
(4) Glutamic Acid

Explanation: Lysine is a basic amino acid with a positively charged side chain at physiological pH. Valine is hydrophobic, tyrosine is aromatic, and glutamic acid is acidic. The presence of an amino group in lysine’s side chain makes it basic. Correct answer is (1) Lysine.

1. Single Correct Answer: Which amino acid has an acidic side chain?
(1) Lysine
(2) Glutamic Acid
(3) Leucine
(4) Phenylalanine

Explanation: Glutamic acid has a carboxyl group in its side chain, making it acidic at physiological pH. Lysine is basic, leucine is hydrophobic, and phenylalanine is aromatic. Correct answer is (2) Glutamic Acid.

2. Single Correct Answer: Aromatic amino acids include:
(1) Valine and Leucine
(2) Tyrosine and Phenylalanine
(3) Lysine and Arginine
(4) Glutamic Acid and Aspartic Acid

Explanation: Tyrosine and phenylalanine contain aromatic rings in their side chains, classifying them as aromatic amino acids. Correct answer is (2).

3. Single Correct Answer: Hydrophobic amino acid is:
(1) Lysine
(2) Valine
(3) Glutamic Acid
(4) Histidine

Explanation: Valine has a nonpolar side chain, making it hydrophobic. Lysine and histidine are basic, glutamic acid is acidic. Correct answer is (2).

4. Assertion-Reason:
Assertion (A): Lysine is positively charged at pH 7.4.
Reason (R): Its side chain contains an amino group that can accept a proton.
(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: Lysine’s side chain amino group accepts a proton at physiological pH, giving it a positive charge. Hence, R correctly explains A. Correct answer is (1).

5. Single Correct Answer: Which amino acid is zwitterionic at physiological pH?
(1) Lysine
(2) Glutamic Acid
(3) Tyrosine
(4) All of the above

Explanation: All amino acids exist as zwitterions at physiological pH with positively charged amino groups and negatively charged carboxyl groups. Correct answer is (4) All of the above.

6. Single Correct Answer: Which amino acid contains a hydroxyl group in its side chain?
(1) Tyrosine
(2) Lysine
(3) Valine
(4) Glutamic Acid

Explanation: Tyrosine has a phenolic hydroxyl group in its aromatic side chain, distinguishing it from lysine, valine, and glutamic acid. Correct answer is (1).

7. Matching Type: Match column I with column II:
a. Basic amino acid – i. Lysine
b. Acidic amino acid – ii. Glutamic Acid
c. Aromatic amino acid – iii. Tyrosine
d. Hydrophobic amino acid – iv. Valine
(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: Lysine is basic (a-i), glutamic acid is acidic (b-ii), tyrosine is aromatic (c-iii), valine is hydrophobic (d-iv). Correct answer is (1).

8. Fill in the blank: The amino acid with basic side chain that can participate in hydrogen bonding is ______.
(1) Lysine
(2) Valine
(3) Tyrosine
(4) Glutamic Acid

Explanation: Lysine’s side chain amino group can form hydrogen bonds and carries positive charge, making it basic. Correct answer is (1).

9. Single Correct Answer: Which amino acid has aliphatic side chain?
(1) Lysine
(2) Valine
(3) Tyrosine
(4) Glutamic Acid

Explanation: Valine contains an aliphatic nonpolar side chain, classifying it as aliphatic. Correct answer is (2).

10. Choose the correct statements:
(a) Lysine is basic
(b) Glutamic acid is acidic
(c) Tyrosine is hydrophobic
(d) Valine is hydrophobic
(1) a, b, d only
(2) a, c, d only
(3) b, c, d only
(4) a, b, c only

Explanation: Lysine is basic (a), glutamic acid acidic (b), valine hydrophobic (d). Tyrosine is aromatic, not purely hydrophobic. Correct answer is (1) a, b, d only.

Subtopic: Enzyme Catalysis and Energy Diagrams

Keyword Definitions

• Enzyme: Biological catalyst that lowers activation energy of biochemical reactions.

• Activation energy: The minimum energy required to initiate a chemical reaction.

• Exothermic reaction: A reaction that releases energy (usually heat) to its surroundings.

• Endothermic reaction: A reaction that absorbs energy from its surroundings.

• Substrate: The reactant on which an enzyme acts.

• Product: The substance formed as a result of a chemical reaction.

• Transition state: High-energy, unstable state during a reaction before forming the product.

• Potenial energy diagram: A graph showing energy changes during a reaction.

• Activation energy with enzyme: Lowered energy barrier when enzyme is present.

• Activation energy without enzyme: Higher energy barrier in absence of enzyme.

• Catalysis: Acceleration of a chemical reaction by a catalyst (enzyme).

Lead Question – 2016 (Phase 2)

Which of the following describes the given graph correctly: (outside the group)

(1) Exothermic reaction with energy A in absence of enzyme and B in presence of enzyme

(2) Endothermic reaction with energy A in presence of enzyme and B in absence of enzyme

(3) Exothermic reaction with energy A in presence of enzyme and B in absence of enzyme

(4) Endothermic reaction with energy A in absence of enzyme and B in presence of enzyme

Explanation: The correct answer is (1): the graph shows an exothermic reaction where energy A represents the activation energy without enzyme and energy B with enzyme. Enzymes lower the activation energy, making product formation faster but not altering overall energy change.

1. Enzyme catalysts increase reaction rate by:

a) Raising activation energy

b) Lowering activation energy

c) Increasing product energy

d) Consuming substrate

Explanation: Enzyme catalysts work by lowering activation energy, allowing reactions to proceed faster and under milder conditions—this is essential for life processes in cells.

2. In a clinical test, elevated activation energy means:

a) Absence of enzyme activity

b) Substrate saturation

c) Increased product concentration

d) Lower reaction temperature

Explanation: High activation energy indicates insufficient enzyme activity, which can signal metabolic disorders or enzyme deficiencies in biological systems.

3. Which part of the graph marks the transition state?

a) At peak energy

b) At substrate level

c) At product level

d) At halfway point

Explanation: The transition state corresponds to the peak of the energy curve, representing an unstable, high-energy configuration before product formation.

4. If a reaction is exothermic, the product level on the graph will be:

a) Higher than substrate

b) Equal to substrate

c) Lower than substrate

d) Cannot be determined

Explanation: In an exothermic reaction, the product energy is lower than substrate energy—the graph’s tail for product is below that for substrate.

5. Which enzyme dysfunction could slow down exothermic metabolic reactions in cells?

a) Hexokinase deficiency

b) Amylase overproduction

c) Pepsin excess

d) Trypsin inactivity

Explanation: Hexokinase is critical for glucose metabolism; its deficiency raises activation energy, slowing exothermic pathways in clinical scenarios like glycogen storage disease.

6. The shape of enzyme active site determines:

a) Activation energy raised

b) Substrate specificity

c) Reaction exothermicity

d) Product energy level

Explanation: The shape of the enzyme’s active site confers substrate specificity, ensuring efficient catalysis and selectivity inside biological systems.

7. Assertion (A): Enzymes do not alter the free energy change of a reaction.

Reason (R): Enzymes lower the activation energy required for the reaction.

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) Both A and R are false

Explanation: Both statements are true. Enzymes only lower the energy barrier (activation energy) and do not affect net energy released or absorbed.

8. Match the following:

Column I

A. Substrate

B. Transition State

C. Product

D. Activation energy

Column II

1. Peak of graph

2. Reactant at start

3. Final lowered energy

4. Difference between substrate and highest point

a) A-2, B-1, C-3, D-4

b) A-1, B-2, C-4, D-3

c) A-3, B-4, C-2, D-1

d) A-4, B-3, C-1, D-2

Explanation: Correct match: A-2 (substrate starts), B-1 (peak), C-3 (product), D-4 (energy difference from substrate to peak).

9. Fill in the blank:

Enzyme presence __________ activation energy for reactions.

a) Increases

b) Maintains

c) Lowers

d) Reverses

Explanation: Enzymes lower activation energy, ensuring biochemical reactions proceed under conditions compatible with life.

10. Choose the correct statements:

I. Enzymes speed up reactions by lowering activation energy.

II. Enzymes make exothermic reactions endothermic.

III. Enzyme does not change net energy in a reaction.

IV. Enzyme converts all substrates irrespective of shape.

a) I and II

b) I and III

c) II and IV

d) I and IV

Explanation: Only statements I and III are correct. Enzymes lower activation energy and do not change overall energy change, but their action is specific to substrate’s shape. 

Subtopic: Protein Structure and Function

Keyword Definitions:

- Protein folding: Process by which a protein assumes its functional three-dimensional structure.

- Hydrogen bond: Weak interaction between polar groups stabilizing secondary and tertiary protein structure.

- Electrostatic interaction: Attraction between charged amino acid side chains aiding protein stability.

- Hydrophobic interaction: Non-polar side chains cluster internally to avoid water, stabilizing tertiary structure.

- Ester bond: Covalent bond between alcohol and acid, rare in protein backbone stabilization.

- Primary structure: Linear sequence of amino acids.

- Secondary structure: α-helix and β-sheet arrangements stabilized by hydrogen bonds.

- Tertiary structure: Overall 3D conformation stabilized by multiple interactions.

Lead Question - 2016 (Phase 2)

Which of the following is the least likely to be involved in stabilizing the three-dimensional folding of most proteins:

(1) Ester bonds

(2) Hydrogen bonds

(3) Electrostatic interaction

(4) Hydrophobic interaction

Answer & Explanation:

Correct answer: Ester bonds. Protein tertiary structure is stabilized by hydrogen bonds, electrostatic interactions, and hydrophobic interactions. Ester bonds rarely occur in the peptide backbone or side chains and are not involved in typical protein folding, making them the least likely contributor to three-dimensional protein stabilization.

1. Which bond is primarily responsible for α-helix formation?

(1) Covalent bond

(2) Hydrogen bond

(3) Ionic bond

(4) Ester bond

Answer & Explanation:

Hydrogen bonds stabilize α-helix secondary structures by linking carbonyl oxygen of one amino acid to amide hydrogen of another. This repetitive bonding maintains helical shape, crucial for protein function and structural integrity.

2. Assertion (A): Hydrophobic interactions drive protein folding.

Reason (R): Non-polar residues avoid water and cluster inside the protein.

(1) Both A and R are true, and R is correct explanation of A

(2) Both A and R are true, but R is not correct explanation of A

(3) A is true, R is false

(4) A is false, R is true

Answer & Explanation:

Both A and R are true, and R is the correct explanation of A. Hydrophobic amino acids cluster internally in aqueous environments, minimizing contact with water, which drives correct protein folding and contributes to tertiary structure stability.

3. Match the bond/interactions with their protein function:

A. Hydrogen bond - (i) Secondary structure

B. Disulfide bond - (ii) Tertiary stability

C. Hydrophobic interaction - (iii) Core packing

(1) A-i, B-ii, C-iii

(2) A-ii, B-iii, C-i

(3) A-iii, B-i, C-ii

(4) A-i, B-iii, C-ii

Answer & Explanation:

Correct answer: A-i, B-ii, C-iii. Hydrogen bonds stabilize α-helices and β-sheets, disulfide bonds covalently reinforce tertiary structure, and hydrophobic interactions pack non-polar residues inside the protein, ensuring structural integrity and functional conformation.

4. Fill in the blank:

The covalent bond that links two cysteine residues is called ________.

(1) Hydrogen bond

(2) Peptide bond

(3) Disulfide bond

(4) Ionic bond

Answer & Explanation:

Disulfide bonds form between two cysteine thiol groups, stabilizing tertiary and quaternary protein structures. These covalent bonds are important in extracellular proteins and contribute to protein resistance against denaturation.

5. Clinical-type Question:

Mutation disrupting hydrogen bonds in hemoglobin can cause:

(1) Sickle cell anemia

(2) Hypertension

(3) Diabetes

(4) Hypercholesterolemia

Answer & Explanation:

Disruption of hydrogen bonding in hemoglobin due to mutation leads to sickle cell anemia. The altered tertiary structure causes hemoglobin polymerization, deformed erythrocytes, reduced oxygen transport, and clinical symptoms such as anemia, pain, and organ damage.

6. Which interaction is key for tertiary protein folding in aqueous environments?

(1) Covalent peptide bond

(2) Hydrogen bond

(3) Hydrophobic interaction

(4) Ester bond

Answer & Explanation:

Hydrophobic interactions are crucial for tertiary folding. Non-polar residues aggregate internally, avoiding water, while polar residues remain exposed. This stabilizes the 3D protein conformation and ensures functional protein architecture.

7. Which bonds/interactions are non-covalent?

(1) Disulfide

(2) Hydrogen, electrostatic, hydrophobic

(3) Peptide

(4) Ester

Answer & Explanation:

Hydrogen bonds, electrostatic interactions, and hydrophobic interactions are non-covalent. They stabilize secondary and tertiary structures without forming permanent covalent linkages, allowing dynamic flexibility and proper protein folding.

8. Choose the correct statements:

(a) Ester bonds rarely stabilize proteins

(b) Hydrophobic interactions stabilize protein core

(c) Electrostatic interactions involve charged residues

(d) All bonds equally contribute to folding

Answer & Explanation:

Correct statements are a, b, and c. Ester bonds are uncommon in proteins, hydrophobic interactions stabilize the interior, and electrostatic interactions between charged side chains support tertiary structure. Not all bonds contribute equally to folding.

9. Which interaction stabilizes β-sheet secondary structures?

(1) Hydrophobic interactions

(2) Hydrogen bonds

(3) Ionic bonds

(4) Disulfide bonds

Answer & Explanation:

Hydrogen bonds between backbone carbonyl and amide groups stabilize β-sheets. This contributes to protein secondary structure, maintaining proper alignment and strength essential for functional domains.

10. Why are protein folding defects clinically significant?

(1) Cause energy deficiency

(2) Lead to misfolded proteins and diseases

(3) Affect DNA replication

(4) Reduce mRNA synthesis

Answer & Explanation:

Misfolded proteins due to defective folding can aggregate, causing diseases like Alzheimer’s, Parkinson’s, and cystic fibrosis. Proper folding is crucial for enzymatic activity, signaling, and structural roles, making understanding protein stabilization essential for clinical interventions.

Topic: Enzymes

Subtopic: Non-Proteinaceous Enzymes

Keyword Definitions:

• Enzyme: Biological catalysts that speed up chemical reactions in living organisms.

• Non-Proteinaceous Enzyme: Enzymes not made of protein but RNA with catalytic activity.

• Deoxyribonuclease (DNase): Enzyme that breaks down DNA into nucleotides.

• Lysozyme: Enzyme that breaks down bacterial cell walls, antimicrobial function.

• Ribozyme: RNA molecule capable of catalyzing specific biochemical reactions.

• Ligase: Enzyme that joins two molecules, usually DNA strands.

Lead Question - 2016 (Phase 2):

A non-proteinaceous enzyme is

(1) Deoxyribonuclease

(2) Lysozyme

(3) Ribozyme

(4) Ligase

Explanation: A non-proteinaceous enzyme is an RNA molecule with catalytic activity, termed a ribozyme. Unlike typical enzymes composed of proteins, ribozymes catalyze reactions using RNA. Therefore, the correct answer is (3) Ribozyme. This concept is fundamental for understanding enzyme diversity in NEET UG biochemistry.

1. Single Correct Answer MCQ:

Which of the following is a proteinaceous enzyme?

(1) Ribozyme

(2) Lysozyme

(3) Hammerhead RNA

(4) Group I intron

Explanation: Lysozyme is a proteinaceous enzyme that breaks down bacterial cell walls. Ribozymes like hammerhead RNA and group I intron are RNA molecules with catalytic function, not proteins. The correct answer is (2) Lysozyme, essential knowledge for distinguishing enzyme types in NEET UG syllabus.

2. Single Correct Answer MCQ:

What is the role of ribozymes in cells?

(1) Catalyze DNA replication

(2) Act as structural proteins

(3) Catalyze RNA splicing and peptide bond formation

(4) Store genetic information

Explanation: Ribozymes catalyze RNA splicing and peptide bond formation during translation and other biochemical reactions. They are functional RNA molecules, not proteins. Thus, the correct answer is (3) Catalyze RNA splicing and peptide bond formation, a crucial concept in molecular biology for NEET UG.

3. Single Correct Answer MCQ:

Deoxyribonuclease (DNase) is composed of

(1) Protein

(2) RNA

(3) Lipids

(4) Carbohydrates

Explanation: DNase is a protein-based enzyme responsible for breaking down DNA into nucleotides. It is not RNA-based, so it's not a ribozyme. The correct answer is (1) Protein, foundational knowledge in biochemistry for NEET UG.

4. Single Correct Answer MCQ:

Which of the following is true about lysozyme?

(1) RNA molecule

(2) Non-proteinaceous enzyme

(3) Protein enzyme degrading bacterial walls

(4) Catalyzes RNA splicing

Explanation: Lysozyme is a protein enzyme that degrades bacterial cell walls by hydrolyzing peptidoglycan. It is not an RNA molecule or ribozyme. The correct answer is (3) Protein enzyme degrading bacterial walls, important for understanding antimicrobial enzymes in NEET UG.

5. Single Correct Answer MCQ (Clinical-type):

Why is ribozyme knowledge important in clinical research?

(1) DNA replication studies

(2) RNA interference and gene therapy

(3) Enzyme replacement therapy

(4) Protein synthesis analysis

Explanation: Ribozymes are utilized in RNA interference and gene therapy to target and cleave specific RNA sequences, offering therapeutic applications in genetic disorders. This non-protein enzymatic mechanism is crucial in modern molecular medicine. The correct answer is (2) RNA interference and gene therapy.

6. Single Correct Answer MCQ:

Ligase functions to

(1) Cleave DNA strands

(2) Join DNA strands

(3) Splice RNA introns

(4) Hydrolyze proteins

Explanation: Ligase catalyzes the joining of DNA strands by forming phosphodiester bonds, important in DNA replication and repair. It is a protein enzyme, not a ribozyme. Therefore, the correct answer is (2) Join DNA strands, key for NEET UG molecular biology preparation.

7. Assertion-Reason MCQ:

Assertion (A): Ribozymes are non-proteinaceous enzymes.

Reason (R): They consist of RNA molecules with catalytic properties.

(1) Both A and R are true and R is correct explanation of A

(2) Both A and R are true but R is not correct explanation of A

(3) A is true but R is false

(4) A is false but R is true

Explanation: Both assertion and reason are correct, and the reason correctly explains the assertion. Ribozymes are RNA molecules capable of catalyzing biochemical reactions, differing from protein enzymes. Thus, the correct answer is (1) Both A and R are true and R is correct explanation of A.

8. Matching Type MCQ:

Match the enzyme with its type:

A. Ribozyme

B. Lysozyme

C. DNase

D. Ligase

1. Non-proteinaceous enzyme

2. Protein enzyme degrading bacterial walls

3. Protein enzyme cleaving DNA

4. Protein enzyme joining DNA strands

Options:

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

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

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

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

Explanation: The correct match is A-1 (Ribozyme-non-proteinaceous enzyme), B-2 (Lysozyme-protein enzyme degrading bacterial walls), C-3 (DNase-protein enzyme cleaving DNA), D-4 (Ligase-protein enzyme joining DNA strands). Thus, the correct answer is (1) A-1, B-2, C-3, D-4.

9. Fill in the Blanks MCQ:

A ribozyme is composed of ______.

(1) Protein

(2) RNA

(3) Lipids

(4) Carbohydrates

Explanation: A ribozyme is an RNA molecule that catalyzes biochemical reactions, acting as a non-protein enzyme. It is crucial in RNA splicing and gene regulation. Therefore, the correct answer is (2) RNA, fundamental knowledge for NEET UG molecular biology.

10. Choose the Correct Statements MCQ:

Select correct statements regarding ribozymes:

(1) They are non-proteinaceous

(2) Composed of RNA

(3) Participate in DNA replication

(4) Involved in RNA splicing

Options:

(1) 1, 2, and 4 only

(2) 1 and 3 only

(3) 2 and 4 only

(4) All statements are correct

Explanation: Statements 1, 2, and 4 are correct. Ribozymes are non-proteinaceous, RNA-based, and involved in RNA splicing. They do not participate directly in DNA replication. Therefore, the correct answer is (1) 1, 2, and 4 only, essential for NEET UG biochemistry preparation.

Subtopic: Enzyme Catalysis and Energy Diagrams

Keyword Definitions

• Enzyme: Biological catalyst that lowers activation energy of biochemical reactions.

• Activation energy: The minimum energy required to initiate a chemical reaction.

• Exothermic reaction: A reaction that releases energy (usually heat) to its surroundings.

• Endothermic reaction: A reaction that absorbs energy from its surroundings.

• Substrate: The reactant on which an enzyme acts.

• Product: The substance formed as a result of a chemical reaction.

• Transition state: High-energy, unstable state during a reaction before forming the product.

• Potenial energy diagram: A graph showing energy changes during a reaction.

• Activation energy with enzyme: Lowered energy barrier when enzyme is present.

• Activation energy without enzyme: Higher energy barrier in absence of enzyme.

• Catalysis: Acceleration of a chemical reaction by a catalyst (enzyme).

Lead Question – 2016 (Phase 2)

Which of the following describes the given graph correctly: (outside the group)

(1) Exothermic reaction with energy A in absence of enzyme and B in presence of enzyme

(2) Endothermic reaction with energy A in presence of enzyme and B in absence of enzyme

(3) Exothermic reaction with energy A in presence of enzyme and B in absence of enzyme

(4) Endothermic reaction with energy A in absence of enzyme and B in presence of enzyme

Explanation: The correct answer is (1): the graph shows an exothermic reaction where energy A represents the activation energy without enzyme and energy B with enzyme. Enzymes lower the activation energy, making product formation faster but not altering overall energy change.

1. Enzyme catalysts increase reaction rate by:

a) Raising activation energy

b) Lowering activation energy

c) Increasing product energy

d) Consuming substrate

Explanation: Enzyme catalysts work by lowering activation energy, allowing reactions to proceed faster and under milder conditions—this is essential for life processes in cells.

2. In a clinical test, elevated activation energy means:

a) Absence of enzyme activity

b) Substrate saturation

c) Increased product concentration

d) Lower reaction temperature

Explanation: High activation energy indicates insufficient enzyme activity, which can signal metabolic disorders or enzyme deficiencies in biological systems.

3. Which part of the graph marks the transition state?

a) At peak energy

b) At substrate level

c) At product level

d) At halfway point

Explanation: The transition state corresponds to the peak of the energy curve, representing an unstable, high-energy configuration before product formation.

4. If a reaction is exothermic, the product level on the graph will be:

a) Higher than substrate

b) Equal to substrate

c) Lower than substrate

d) Cannot be determined

Explanation: In an exothermic reaction, the product energy is lower than substrate energy—the graph’s tail for product is below that for substrate.

5. Which enzyme dysfunction could slow down exothermic metabolic reactions in cells?

a) Hexokinase deficiency

b) Amylase overproduction

c) Pepsin excess

d) Trypsin inactivity

Explanation: Hexokinase is critical for glucose metabolism; its deficiency raises activation energy, slowing exothermic pathways in clinical scenarios like glycogen storage disease.

6. The shape of enzyme active site determines:

a) Activation energy raised

b) Substrate specificity

c) Reaction exothermicity

d) Product energy level

Explanation: The shape of the enzyme’s active site confers substrate specificity, ensuring efficient catalysis and selectivity inside biological systems.

7. Assertion (A): Enzymes do not alter the free energy change of a reaction.

Reason (R): Enzymes lower the activation energy required for the reaction.

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) Both A and R are false

Explanation: Both statements are true. Enzymes only lower the energy barrier (activation energy) and do not affect net energy released or absorbed.

8. Match the following:

Column I

A. Substrate

B. Transition State

C. Product

D. Activation energy

Column II

1. Peak of graph

2. Reactant at start

3. Final lowered energy

4. Difference between substrate and highest point

a) A-2, B-1, C-3, D-4

b) A-1, B-2, C-4, D-3

c) A-3, B-4, C-2, D-1

d) A-4, B-3, C-1, D-2

Explanation: Correct match: A-2 (substrate starts), B-1 (peak), C-3 (product), D-4 (energy difference from substrate to peak).

9. Fill in the blank:

Enzyme presence __________ activation energy for reactions.

a) Increases

b) Maintains

c) Lowers

d) Reverses

Explanation: Enzymes lower activation energy, ensuring biochemical reactions proceed under conditions compatible with life.

10. Choose the correct statements:

I. Enzymes speed up reactions by lowering activation energy.

II. Enzymes make exothermic reactions endothermic.

III. Enzyme does not change net energy in a reaction.

IV. Enzyme converts all substrates irrespective of shape.

a) I and II

b) I and III

c) II and IV

d) I and IV

Explanation: Only statements I and III are correct. Enzymes lower activation energy and do not change overall energy change, but their action is specific to substrate’s shape. 

Subtopic: Protein Structure and Function

Keyword Definitions:

- Protein folding: Process by which a protein assumes its functional three-dimensional structure.

- Hydrogen bond: Weak interaction between polar groups stabilizing secondary and tertiary protein structure.

- Electrostatic interaction: Attraction between charged amino acid side chains aiding protein stability.

- Hydrophobic interaction: Non-polar side chains cluster internally to avoid water, stabilizing tertiary structure.

- Ester bond: Covalent bond between alcohol and acid, rare in protein backbone stabilization.

- Primary structure: Linear sequence of amino acids.

- Secondary structure: α-helix and β-sheet arrangements stabilized by hydrogen bonds.

- Tertiary structure: Overall 3D conformation stabilized by multiple interactions.

Lead Question - 2016 (Phase 2)

Which of the following is the least likely to be involved in stabilizing the three-dimensional folding of most proteins:

(1) Ester bonds

(2) Hydrogen bonds

(3) Electrostatic interaction

(4) Hydrophobic interaction

Answer & Explanation:

Correct answer: Ester bonds. Protein tertiary structure is stabilized by hydrogen bonds, electrostatic interactions, and hydrophobic interactions. Ester bonds rarely occur in the peptide backbone or side chains and are not involved in typical protein folding, making them the least likely contributor to three-dimensional protein stabilization.

1. Which bond is primarily responsible for α-helix formation?

(1) Covalent bond

(2) Hydrogen bond

(3) Ionic bond

(4) Ester bond

Answer & Explanation:

Hydrogen bonds stabilize α-helix secondary structures by linking carbonyl oxygen of one amino acid to amide hydrogen of another. This repetitive bonding maintains helical shape, crucial for protein function and structural integrity.

2. Assertion (A): Hydrophobic interactions drive protein folding.

Reason (R): Non-polar residues avoid water and cluster inside the protein.

(1) Both A and R are true, and R is correct explanation of A

(2) Both A and R are true, but R is not correct explanation of A

(3) A is true, R is false

(4) A is false, R is true

Answer & Explanation:

Both A and R are true, and R is the correct explanation of A. Hydrophobic amino acids cluster internally in aqueous environments, minimizing contact with water, which drives correct protein folding and contributes to tertiary structure stability.

3. Match the bond/interactions with their protein function:

A. Hydrogen bond - (i) Secondary structure

B. Disulfide bond - (ii) Tertiary stability

C. Hydrophobic interaction - (iii) Core packing

(1) A-i, B-ii, C-iii

(2) A-ii, B-iii, C-i

(3) A-iii, B-i, C-ii

(4) A-i, B-iii, C-ii

Answer & Explanation:

Correct answer: A-i, B-ii, C-iii. Hydrogen bonds stabilize α-helices and β-sheets, disulfide bonds covalently reinforce tertiary structure, and hydrophobic interactions pack non-polar residues inside the protein, ensuring structural integrity and functional conformation.

4. Fill in the blank:

The covalent bond that links two cysteine residues is called ________.

(1) Hydrogen bond

(2) Peptide bond

(3) Disulfide bond

(4) Ionic bond

Answer & Explanation:

Disulfide bonds form between two cysteine thiol groups, stabilizing tertiary and quaternary protein structures. These covalent bonds are important in extracellular proteins and contribute to protein resistance against denaturation.

5. Clinical-type Question:

Mutation disrupting hydrogen bonds in hemoglobin can cause:

(1) Sickle cell anemia

(2) Hypertension

(3) Diabetes

(4) Hypercholesterolemia

Answer & Explanation:

Disruption of hydrogen bonding in hemoglobin due to mutation leads to sickle cell anemia. The altered tertiary structure causes hemoglobin polymerization, deformed erythrocytes, reduced oxygen transport, and clinical symptoms such as anemia, pain, and organ damage.

6. Which interaction is key for tertiary protein folding in aqueous environments?

(1) Covalent peptide bond

(2) Hydrogen bond

(3) Hydrophobic interaction

(4) Ester bond

Answer & Explanation:

Hydrophobic interactions are crucial for tertiary folding. Non-polar residues aggregate internally, avoiding water, while polar residues remain exposed. This stabilizes the 3D protein conformation and ensures functional protein architecture.

7. Which bonds/interactions are non-covalent?

(1) Disulfide

(2) Hydrogen, electrostatic, hydrophobic

(3) Peptide

(4) Ester

Answer & Explanation:

Hydrogen bonds, electrostatic interactions, and hydrophobic interactions are non-covalent. They stabilize secondary and tertiary structures without forming permanent covalent linkages, allowing dynamic flexibility and proper protein folding.

8. Choose the correct statements:

(a) Ester bonds rarely stabilize proteins

(b) Hydrophobic interactions stabilize protein core

(c) Electrostatic interactions involve charged residues

(d) All bonds equally contribute to folding

Answer & Explanation:

Correct statements are a, b, and c. Ester bonds are uncommon in proteins, hydrophobic interactions stabilize the interior, and electrostatic interactions between charged side chains support tertiary structure. Not all bonds contribute equally to folding.

9. Which interaction stabilizes β-sheet secondary structures?

(1) Hydrophobic interactions

(2) Hydrogen bonds

(3) Ionic bonds

(4) Disulfide bonds

Answer & Explanation:

Hydrogen bonds between backbone carbonyl and amide groups stabilize β-sheets. This contributes to protein secondary structure, maintaining proper alignment and strength essential for functional domains.

10. Why are protein folding defects clinically significant?

(1) Cause energy deficiency

(2) Lead to misfolded proteins and diseases

(3) Affect DNA replication

(4) Reduce mRNA synthesis

Answer & Explanation:

Misfolded proteins due to defective folding can aggregate, causing diseases like Alzheimer’s, Parkinson’s, and cystic fibrosis. Proper folding is crucial for enzymatic activity, signaling, and structural roles, making understanding protein stabilization essential for clinical interventions.

Topic: Enzymes

Subtopic: Non-Proteinaceous Enzymes

Keyword Definitions:

• Enzyme: Biological catalysts that speed up chemical reactions in living organisms.

• Non-Proteinaceous Enzyme: Enzymes not made of protein but RNA with catalytic activity.

• Deoxyribonuclease (DNase): Enzyme that breaks down DNA into nucleotides.

• Lysozyme: Enzyme that breaks down bacterial cell walls, antimicrobial function.

• Ribozyme: RNA molecule capable of catalyzing specific biochemical reactions.

• Ligase: Enzyme that joins two molecules, usually DNA strands.

Lead Question - 2016 (Phase 2):

A non-proteinaceous enzyme is

(1) Deoxyribonuclease

(2) Lysozyme

(3) Ribozyme

(4) Ligase

Explanation: A non-proteinaceous enzyme is an RNA molecule with catalytic activity, termed a ribozyme. Unlike typical enzymes composed of proteins, ribozymes catalyze reactions using RNA. Therefore, the correct answer is (3) Ribozyme. This concept is fundamental for understanding enzyme diversity in NEET UG biochemistry.

1. Single Correct Answer MCQ:

Which of the following is a proteinaceous enzyme?

(1) Ribozyme

(2) Lysozyme

(3) Hammerhead RNA

(4) Group I intron

Explanation: Lysozyme is a proteinaceous enzyme that breaks down bacterial cell walls. Ribozymes like hammerhead RNA and group I intron are RNA molecules with catalytic function, not proteins. The correct answer is (2) Lysozyme, essential knowledge for distinguishing enzyme types in NEET UG syllabus.

2. Single Correct Answer MCQ:

What is the role of ribozymes in cells?

(1) Catalyze DNA replication

(2) Act as structural proteins

(3) Catalyze RNA splicing and peptide bond formation

(4) Store genetic information

Explanation: Ribozymes catalyze RNA splicing and peptide bond formation during translation and other biochemical reactions. They are functional RNA molecules, not proteins. Thus, the correct answer is (3) Catalyze RNA splicing and peptide bond formation, a crucial concept in molecular biology for NEET UG.

3. Single Correct Answer MCQ:

Deoxyribonuclease (DNase) is composed of

(1) Protein

(2) RNA

(3) Lipids

(4) Carbohydrates

Explanation: DNase is a protein-based enzyme responsible for breaking down DNA into nucleotides. It is not RNA-based, so it's not a ribozyme. The correct answer is (1) Protein, foundational knowledge in biochemistry for NEET UG.

4. Single Correct Answer MCQ:

Which of the following is true about lysozyme?

(1) RNA molecule

(2) Non-proteinaceous enzyme

(3) Protein enzyme degrading bacterial walls

(4) Catalyzes RNA splicing

Explanation: Lysozyme is a protein enzyme that degrades bacterial cell walls by hydrolyzing peptidoglycan. It is not an RNA molecule or ribozyme. The correct answer is (3) Protein enzyme degrading bacterial walls, important for understanding antimicrobial enzymes in NEET UG.

5. Single Correct Answer MCQ (Clinical-type):

Why is ribozyme knowledge important in clinical research?

(1) DNA replication studies

(2) RNA interference and gene therapy

(3) Enzyme replacement therapy

(4) Protein synthesis analysis

Explanation: Ribozymes are utilized in RNA interference and gene therapy to target and cleave specific RNA sequences, offering therapeutic applications in genetic disorders. This non-protein enzymatic mechanism is crucial in modern molecular medicine. The correct answer is (2) RNA interference and gene therapy.

6. Single Correct Answer MCQ:

Ligase functions to

(1) Cleave DNA strands

(2) Join DNA strands

(3) Splice RNA introns

(4) Hydrolyze proteins

Explanation: Ligase catalyzes the joining of DNA strands by forming phosphodiester bonds, important in DNA replication and repair. It is a protein enzyme, not a ribozyme. Therefore, the correct answer is (2) Join DNA strands, key for NEET UG molecular biology preparation.

7. Assertion-Reason MCQ:

Assertion (A): Ribozymes are non-proteinaceous enzymes.

Reason (R): They consist of RNA molecules with catalytic properties.

(1) Both A and R are true and R is correct explanation of A

(2) Both A and R are true but R is not correct explanation of A

(3) A is true but R is false

(4) A is false but R is true

Explanation: Both assertion and reason are correct, and the reason correctly explains the assertion. Ribozymes are RNA molecules capable of catalyzing biochemical reactions, differing from protein enzymes. Thus, the correct answer is (1) Both A and R are true and R is correct explanation of A.

8. Matching Type MCQ:

Match the enzyme with its type:

A. Ribozyme

B. Lysozyme

C. DNase

D. Ligase

1. Non-proteinaceous enzyme

2. Protein enzyme degrading bacterial walls

3. Protein enzyme cleaving DNA

4. Protein enzyme joining DNA strands

Options:

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

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

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

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

Explanation: The correct match is A-1 (Ribozyme-non-proteinaceous enzyme), B-2 (Lysozyme-protein enzyme degrading bacterial walls), C-3 (DNase-protein enzyme cleaving DNA), D-4 (Ligase-protein enzyme joining DNA strands). Thus, the correct answer is (1) A-1, B-2, C-3, D-4.

9. Fill in the Blanks MCQ:

A ribozyme is composed of ______.

(1) Protein

(2) RNA

(3) Lipids

(4) Carbohydrates

Explanation: A ribozyme is an RNA molecule that catalyzes biochemical reactions, acting as a non-protein enzyme. It is crucial in RNA splicing and gene regulation. Therefore, the correct answer is (2) RNA, fundamental knowledge for NEET UG molecular biology.

10. Choose the Correct Statements MCQ:

Select correct statements regarding ribozymes:

(1) They are non-proteinaceous

(2) Composed of RNA

(3) Participate in DNA replication

(4) Involved in RNA splicing

Options:

(1) 1, 2, and 4 only

(2) 1 and 3 only

(3) 2 and 4 only

(4) All statements are correct

Explanation: Statements 1, 2, and 4 are correct. Ribozymes are non-proteinaceous, RNA-based, and involved in RNA splicing. They do not participate directly in DNA replication. Therefore, the correct answer is (1) 1, 2, and 4 only, essential for NEET UG biochemistry preparation.

Topic: Lipids
Subtopic: Structure and Types of Fats

Keywords:
Fat Molecule: Organic compound made of glycerol and fatty acids.
Glycerol: Three-carbon alcohol forming backbone of fats.
Fatty Acid: Long-chain carboxylic acids in fats.
Triglyceride: Typical fat with one glycerol and three fatty acids.
Atypical Fat: Fat molecule with unusual combination of glycerol and fatty acids.
Saturated Fat: Fat with no double bonds in fatty acids.
Unsaturated Fat: Fat containing one or more double bonds in fatty acids.
Phospholipid: Lipid with phosphate group, forming cell membranes.
Metabolic Relevance: Fats provide energy and store nutrients.
Clinical Relevance: Abnormal fat types may affect obesity, cardiovascular health, or lipid metabolism disorders.
Lipid Metabolism: Biochemical process involving fat synthesis and breakdown.

Lead Question - 2016 (Phase 1)
Atypical fat molecule is made up of:
(1) Three glycerol molecules and one fatty acid molecule
(2) One glycerol and three fatty acid molecules
(3) One glycerol and one fatty acid molecule
(4) Three glycerol and three fatty acid molecules
Answer & Explanation: Option 1. Atypical fats have unusual structures, such as multiple glycerol molecules linked to fewer fatty acids. Here, three glycerol molecules combine with one fatty acid, creating a non-standard lipid. Such molecules can influence metabolic pathways, energy storage, and may have specialized biological or clinical roles.

Question 1: Typical triglycerides consist of:
A. One glycerol and one fatty acid
B. Three glycerol and three fatty acids
C. One glycerol and three fatty acids
D. Three glycerol and one fatty acid
Answer & Explanation: Option C. Triglycerides are the most common fats in animals and plants. One glycerol molecule esterifies with three fatty acids. They store energy efficiently, provide insulation, and serve as precursors for signaling molecules in metabolism.

Question 2: Unsaturated fats differ from saturated fats because they:
A. Contain double bonds in fatty acids
B. Have no glycerol backbone
C. Cannot be digested
D. Always exist as solids
Answer & Explanation: Option A. Unsaturated fats contain one or more double bonds in fatty acid chains, creating kinks that prevent tight packing. This makes them liquid at room temperature and metabolically distinct, affecting cardiovascular health and membrane fluidity.

Question 3: Phospholipids are crucial because they:
A. Store energy only
B. Form cell membranes
C. Are always atypical fats
D. Cause obesity directly
Answer & Explanation: Option B. Phospholipids contain glycerol, two fatty acids, and a phosphate group. They are amphipathic, forming bilayers essential for cell membranes. Their structure allows selective permeability and signaling in cells.

Question 4: Atypical fats with multiple glycerols may influence:
A. DNA replication
B. Lipid metabolism
C. Protein translation
D. Ribosome assembly
Answer & Explanation: Option B. Atypical fats alter metabolic pathways by affecting enzyme recognition, energy storage, and lipid signaling. Their unusual structure can influence digestion, absorption, and clinical outcomes related to obesity or lipid disorders.

Question 5: Clinical importance of fat structure includes:
A. Energy storage
B. Membrane function
C. Risk of cardiovascular disease
D. All of the above
Answer & Explanation: Option D. Fats provide stored energy, are essential components of cell membranes, and abnormal types or excess accumulation can contribute to metabolic disorders, obesity, and cardiovascular diseases, making structural understanding clinically relevant.

Question 6: Esterification in fat formation links:
A. Glycerol and phosphate
B. Fatty acids and amino acids
C. Glycerol and fatty acids
D. Nucleotides and sugars
Answer & Explanation: Option C. Ester bonds form between the hydroxyl groups of glycerol and carboxyl groups of fatty acids during fat synthesis. This reaction is catalyzed by enzymes in lipid metabolism, producing energy storage molecules and maintaining membrane structures.

Question 7 (Assertion-Reason):
Assertion (A): Atypical fats may contain multiple glycerol molecules.
Reason (R): Standard triglycerides contain only one glycerol and three fatty acids.
A. Both A and R are true, and R is the correct explanation of A
B. Both A and R are true, but 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 A. Typical triglycerides have one glycerol and three fatty acids. Atypical fats deviate from this structure, often having multiple glycerols linked to fewer fatty acids. Understanding this difference is crucial for biochemical and clinical implications.

Question 8 (Matching Type):
Match the lipid type with its feature:
Column A:
1. Triglyceride
2. Phospholipid
3. Atypical fat
4. Polyunsaturated fat
Column B:
A. Contains phosphate group, forms membranes
B. One glycerol and three fatty acids
C. Multiple glycerols or unusual structure
D. Contains multiple double bonds
Answer & Explanation:
1-B, 2-A, 3-C, 4-D. Triglycerides are standard storage fats; phospholipids build membranes; atypical fats have unusual glycerol/fatty acid combinations; polyunsaturated fats have multiple double bonds, influencing fluidity and metabolism.

Question 9 (Fill in the Blanks):
Atypical fat molecules differ from standard triglycerides in the number of __________.
A. Fatty acids only
B. Glycerol molecules
C. Phosphate groups
D. Carbohydrates
Answer & Explanation: Option B. Atypical fats can have multiple glycerol molecules linked to fewer fatty acids, deviating from standard triglycerides. This affects digestion, energy storage, and biochemical pathways, making their study important for metabolism and clinical applications.

Question 10: Select correct statements about fats:
1. Standard triglycerides have one glycerol and three fatty acids.
2. Atypical fats may have more than one glycerol.
3. Fats are irrelevant for clinical health.
4. Polyunsaturated fats contain double bonds.
A. 1, 2, 3
B. 1, 2, 4
C. 2, 3, 4
D. 1, 3, 4
Answer & Explanation: Option B. Statements 1, 2, and 4 are correct. Standard triglycerides have one glycerol and three fatty acids; atypical fats may have multiple glycerols; polyunsaturated fats contain double bonds. Fats are critical for energy, metabolism, and clinical health, making statement 3 incorrect.

Chapter: Biomolecules

Topic: Carbohydrates, Nucleic Acids, and Amino Acids

Subtopic: Structure and Function of Biomolecules

Keyword Definitions:

• Sucrose: A disaccharide composed of glucose and fructose molecules.

• Cellulose: A polysaccharide made of β-glucose units forming plant cell walls.

• Uracil: A pyrimidine base found in RNA replacing thymine.

• Glycine: The simplest amino acid; non-sulfur containing.

2016 (Phase 1)

Lead Question: Which one of the following statements is wrong:

• (1) Sucrose is a disaccharide.

• (2) Cellulose is a polysaccharide.

• (3) Uracil is a pyrimidine.

• (4) Glycine is a sulfur containing amino acid.

Answer & Explanation: The correct answer is (4). Glycine is the simplest amino acid and does not contain sulfur. Amino acids like cysteine and methionine contain sulfur. Sucrose is correctly a disaccharide, cellulose a polysaccharide, and uracil a pyrimidine base in RNA, making option (4) incorrect.

Keyword Definitions:

• Monosaccharides: Simple sugars like glucose and fructose.

• Polysaccharides: Long carbohydrate chains like starch and glycogen.

2021

Single Correct Answer MCQ: Which of the following is a monosaccharide?

• (1) Sucrose

• (2) Cellulose

• (3) Glucose

• (4) Maltose

Answer & Explanation: The correct answer is (3) Glucose. Glucose is a monosaccharide with the chemical formula C6H12O6, serving as a fundamental energy source for cells. Sucrose and maltose are disaccharides, while cellulose is a polysaccharide used structurally in plant cell walls.

Keyword Definitions:

• Nucleic Acids: DNA and RNA composed of nucleotides carrying genetic information.

• Pyrimidines: Single-ring nitrogenous bases such as uracil, cytosine, and thymine.

2020

Single Correct Answer MCQ: Which pyrimidine is found in RNA but not in DNA?

• (1) Thymine

• (2) Cytosine

• (3) Uracil

• (4) Adenine

Answer & Explanation: The correct answer is (3) Uracil. Uracil is a pyrimidine base present in RNA, replacing thymine found in DNA. It pairs with adenine during RNA synthesis, playing a crucial role in transcription and gene expression.

Keyword Definitions:

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

2019

Single Correct Answer MCQ: Which of the following amino acids contains sulfur?

• (1) Glycine

• (2) Alanine

• (3) Cysteine

• (4) Leucine

Answer & Explanation: The correct answer is (3) Cysteine. Cysteine contains a thiol (-SH) group which includes sulfur, allowing it to form disulfide bonds important for protein structure. Glycine and alanine do not contain sulfur.

Keyword Definitions:

• Disaccharides: Carbohydrates composed of two monosaccharide units.

2018

Single Correct Answer MCQ: Sucrose is formed by the combination of which two monosaccharides?

• (1) Glucose and Galactose

• (2) Glucose and Fructose

• (3) Glucose and Glucose

• (4) Fructose and Galactose

Answer & Explanation: The correct answer is (2) Glucose and Fructose. Sucrose is a disaccharide formed by the condensation of glucose and fructose via a glycosidic bond, commonly found in plants and used as table sugar.

Keyword Definitions:

• Peptide Bond: Covalent bond linking amino acids in proteins.

2017

Single Correct Answer MCQ: Peptide bonds form between:

• (1) Two carboxyl groups

• (2) Amino group of one and carboxyl group of another amino acid

• (3) Two amino groups

• (4) Hydroxyl and amino group

Answer & Explanation: The correct answer is (2). Peptide bonds form through a condensation reaction between the amino group (-NH2) of one amino acid and the carboxyl group (-COOH) of another, creating polypeptides and proteins essential for biological functions.

Keyword Definitions:

• Nucleotides: Monomers of nucleic acids composed of a nitrogenous base, sugar, and phosphate group.

2022

Assertion-Reason MCQ:

Assertion (A): DNA contains thymine, while RNA contains uracil.

Reason (R): Thymine is more stable than uracil in DNA molecules.

• (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 & Explanation: The correct answer is (1). DNA uses thymine because it is chemically more stable than uracil, which prevents mutations over time. RNA uses uracil as a cost-effective substitute since it is not required to be as stable as DNA for transient genetic messages.

Keyword Definitions:

• Polysaccharides: Large carbohydrates formed by multiple monosaccharides.

2015

Matching Type MCQ: Match the carbohydrate with its type:

A. Glucose           1. Polysaccharide

B. Starch            2. Monosaccharide

C. Sucrose           3. Disaccharide

• (1) A-2, B-1, C-3

• (2) A-1, B-3, C-2

• (3) A-3, B-2, C-1

• (4) A-2, B-3, C-1

Answer & Explanation: The correct answer is (1) A-2, B-1, C-3. Glucose is a monosaccharide serving as a fundamental energy source. Starch is a polysaccharide storing energy in plants. Sucrose is a disaccharide composed of glucose and fructose.

Keyword Definitions:

• Essential Amino Acids: Amino acids that cannot be synthesized by the body and must be obtained from the diet.

2018

Fill in the Blanks MCQ: The amino acid __________ is the simplest and does not contain a side chain with sulfur.

• (1) Methionine

• (2) Glycine

• (3) Cysteine

• (4) Alanine

Answer & Explanation: The correct answer is (2) Glycine. Glycine is the simplest amino acid with a single hydrogen atom as its side chain. It does not contain sulfur, unlike cysteine or methionine, which have sulfur-containing side chains important for protein structure and function.

Keyword Definitions:

• Metabolic Disorders: Disorders affecting biochemical processes in the body.

2021

Choose the correct statements MCQ:

• 1. Sucrose is hydrolyzed by sucrase enzyme in the body.

• 2. Uracil is present in both DNA and RNA.

• 3. Cellulose provides structural support in plants.

• 4. Glycine is a sulfur-containing amino acid.

• (1) 1 and 3 only

• (2) 2 and 4 only

• (3) 1, 2, and 3 only

• (4) All statements are correct

Answer & Explanation: The correct answer is (1). Sucrose is hydrolyzed by sucrase into glucose and fructose for absorption. Cellulose provides structural integrity in plant cell walls. Uracil is only in RNA, and glycine lacks sulfur, making statements 2 and 4 incorrect.

Chapter: Biochemistry

Sub-topic: Structure of Proteins and Hormones - Human Insulin

Keyword Definitions:

Polypeptides: Chains of amino acids linked by peptide bonds forming proteins.

Disulphide Bridges: Covalent bonds formed between sulfur atoms of cysteine residues in proteins.

Covalent Bonds: Strong chemical bonds involving sharing of electron pairs between atoms.

Hydrogen Bonds: Weak bonds important in protein secondary and tertiary structure.

Phosphodiester Bond: Covalent bond linking nucleotides in nucleic acids.

Insulin: A peptide hormone regulating glucose metabolism, composed of two polypeptide chains (A and B chains).

Lead Question 2016 (Phase 1):

The two polypeptides of human insulin are linked together by:

A) Hydrogen bonds
B) Phosphodiester bond
C) Covalent bond
D) Disulphide bridges

Answer: D) Disulphide bridges

The two chains (A and B) of insulin are connected by covalent disulphide bridges between cysteine residues. These bridges stabilize insulin's structure and are crucial for its biological activity.

Practice MCQs

1. Which type of bond primarily stabilizes the tertiary structure of insulin?
A) Hydrogen bonds
B) Ionic bonds
C) Disulphide bridges
D) Peptide bonds
Answer: C) Disulphide bridges
Disulphide bridges are covalent bonds between sulfur atoms of cysteine residues and play a key role in maintaining insulin's three-dimensional conformation.

2. Insulin is secreted by which cells of the pancreas?
A) Alpha cells
B) Beta cells
C) Delta cells
D) Acinar cells
Answer: B) Beta cells
Beta cells in the pancreatic islets of Langerhans produce and secrete insulin, which regulates blood glucose levels.

3. The primary structure of insulin is made up of:
A) Carbohydrates
B) Amino acids
C) Fatty acids
D) Nucleotides
Answer: B) Amino acids
Insulin is a protein hormone composed of amino acids linked by peptide bonds forming polypeptide chains.

4. Which organ is primarily responsible for insulin degradation?
A) Liver
B) Kidney
C) Pancreas
D) Muscle
Answer: A) Liver
The liver plays a major role in metabolizing and degrading circulating insulin after it exerts its effects.

5. A mutation disrupting disulphide bond formation in insulin would most likely cause:
A) Increased insulin activity
B) Loss of insulin structure and function
C) Enhanced glucose uptake
D) Increased insulin secretion
Answer: B) Loss of insulin structure and function
Disulphide bonds are critical for insulin’s structural integrity; disruption leads to loss of function and can contribute to diabetes.

6. Assertion-Reason:
Assertion (A): Disulphide bridges are covalent bonds.
Reason (R): They involve sharing of electron pairs between sulfur atoms of cysteine residues.
Options:
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
Answer: A) Both A and R are true, and R explains A
Disulphide bridges are covalent bonds formed by sharing electrons between sulfur atoms of cysteine, explaining their strong, stable nature in proteins like insulin.

7. Match the terms in Column A with their correct descriptions in Column B:

Column A

Column B

1. Polypeptide

B. Chain of amino acids

2. Disulphide bridge

A. Covalent bond linking sulfur atoms

3. Insulin

C. Hormone regulating blood glucose

4. Phosphodiester bond

D. Bond linking nucleotides in DNA/RNA

Answer: 1 → B, 2 → A, 3 → C, 4 → D

8. (Diagram-based MCQ)
The figure shows two polypeptide chains connected by sulfur-sulfur bonds. Which hormone does this structure most likely represent?
A) Growth hormone
B) Insulin
C) Thyroxine
D) Glucagon
Answer: B) Insulin
Insulin consists of two chains (A and B) linked by disulphide bridges, characteristic of its structure.

9. Fill in the blank:
The two chains of human insulin are linked together by _______.
A) Hydrogen bonds
B) Ionic bonds
C) Phosphodiester bonds
D) Disulphide bridges
Answer: D) Disulphide bridges
Disulphide bridges form covalent bonds between cysteine residues stabilizing insulin’s structure.

10. Passage-based MCQ:
Passage: A patient with a mutation affecting cysteine residues in the insulin gene develops symptoms of diabetes mellitus. The mutation prevents the formation of key covalent bonds between insulin chains.
What type of bond is most likely disrupted in this patient?
A) Peptide bond
B) Hydrogen bond
C) Disulphide bridge
D) Phosphodiester bond
Answer: C) Disulphide bridge
Disulphide bridges connect the two insulin polypeptide chains; mutations disrupting these bonds impair insulin structure and function, causing diabetes symptoms.