Subtopic: Neurotransmitter Receptors
Keyword Definitions:
• Ionic receptors: Ligand-gated ion channels that mediate fast synaptic transmission.
• NMDA: A subtype of glutamate receptor functioning as an ion channel.
• Kainate: Ionotropic glutamate receptor subtype controlling sodium influx.
• mGluR: Metabotropic glutamate receptor linked to G-proteins, not ionotropic.
• AMPA: Ionotropic glutamate receptor mediating fast excitatory transmission.
Lead Question - 2013
Ionic receptors are all except ?
a) NMDA
b) Kainate
c) mGluR
d) AMPA
Explanation: Ionotropic receptors are ligand-gated ion channels such as NMDA, Kainate, and AMPA, which mediate rapid excitatory synaptic transmission. Metabotropic glutamate receptors (mGluRs) are G-protein coupled receptors, slower in action and not ionic. Hence, the correct answer is c) mGluR.
1) Guess Question:
Which receptor subtype is blocked by magnesium at rest?
a) AMPA
b) NMDA
c) Kainate
d) mGluR
Explanation: NMDA receptors are blocked by magnesium ions at resting potential. Depolarization removes the block, allowing calcium and sodium influx. This mechanism is crucial for synaptic plasticity. Answer: b) NMDA.
2) Guess Question:
Which receptor subtype mediates most fast excitatory neurotransmission in CNS?
a) NMDA
b) AMPA
c) GABA-A
d) Glycine
Explanation: AMPA receptors mediate the majority of fast excitatory synaptic responses in the central nervous system by allowing sodium influx when glutamate binds. Answer: b) AMPA.
3) Guess Question:
Which neurotransmitter activates NMDA, AMPA, and Kainate receptors?
a) Acetylcholine
b) Glutamate
c) GABA
d) Glycine
Explanation: Glutamate is the major excitatory neurotransmitter in the CNS. It binds to NMDA, AMPA, and Kainate receptors, mediating excitatory neurotransmission and plasticity. Answer: b) Glutamate.
4) Guess Question:
A 65-year-old patient with Alzheimer’s disease benefits from memantine because it blocks:
a) GABA-A
b) NMDA
c) AMPA
d) Kainate
Explanation: Memantine is an NMDA receptor antagonist that reduces excitotoxicity caused by excessive glutamate activity in Alzheimer’s disease. Answer: b) NMDA.
5) Guess Question:
Which receptor subtype is a G-protein coupled receptor (GPCR)?
a) NMDA
b) AMPA
c) Kainate
d) mGluR
Explanation: Metabotropic glutamate receptors (mGluRs) are GPCRs that activate second messenger systems. They are not ionotropic receptors. Answer: d) mGluR.
6) Guess Question:
Inhibition of which receptor improves seizure control in epilepsy?
a) NMDA
b) AMPA
c) Kainate
d) All of the above
Explanation: Excitatory glutamate receptors like NMDA, AMPA, and Kainate are involved in seizure generation. Blocking them reduces excitability, making d) All of the above correct.
7) Guess Question:
A patient with excessive glutamate release may develop:
a) Excitotoxicity
b) Bradycardia
c) Hypoglycemia
d) Alkalosis
Explanation: Excessive glutamate activates ionotropic receptors like NMDA, leading to calcium overload and neuronal damage called excitotoxicity, common in stroke and trauma. Answer: a) Excitotoxicity.
8) Guess Question:
Which ion is mainly conducted by AMPA receptors?
a) Calcium
b) Sodium
c) Potassium
d) Chloride
Explanation: AMPA receptors mainly conduct sodium ions into the neuron, causing depolarization. Some AMPA subtypes may also allow calcium entry. Answer: b) Sodium.
9) Guess Question:
NMDA receptor activation requires binding of:
a) Glutamate only
b) Glycine only
c) Glutamate and glycine
d) GABA
Explanation: NMDA receptors require co-agonist binding of glutamate and glycine for activation. This dual requirement ensures controlled calcium influx. Answer: c) Glutamate and glycine.
10) Guess Question:
A patient on phencyclidine (PCP) shows psychotic symptoms due to blockade of:
a) NMDA receptors
b) AMPA receptors
c) Kainate receptors
d) mGluRs
Explanation: PCP blocks NMDA receptors, impairing glutamate transmission and causing dissociative and psychotic symptoms. Answer: a) NMDA receptors.
Topic: Protein Metabolism
Subtopic: Protein Processing and Glycosylation
Keyword Definitions:
• Protein glycosylation: Process of adding carbohydrate chains to proteins, critical for folding and function.
• Endoplasmic reticulum (ER): Organelle where N-linked glycosylation begins.
• Golgi body: Organelle that modifies and completes glycosylation.
• Ribosome: Organelle responsible for protein synthesis, not glycosylation.
• Cytoplasm: Fluid matrix for biochemical reactions, not glycosylation.
Lead Question - 2013
Major site of protein glycosylation is ?
a) ER and golgi body
b) Ribosome and golgi body
c) ER and ribosome
d) Ribosome and cytoplasm
Explanation: Protein glycosylation occurs mainly in the endoplasmic reticulum and Golgi apparatus. Ribosomes synthesize proteins, while cytoplasm does not play a direct role in glycosylation. The ER initiates N-linked glycosylation, and the Golgi body processes O-linked and complex modifications. Answer: a) ER and golgi body.
1) Guess Question:
Which type of glycosylation starts in the ER?
a) N-linked glycosylation
b) O-linked glycosylation
c) Both
d) None
Explanation: N-linked glycosylation begins in the ER with the attachment of oligosaccharides to asparagine residues. Further processing occurs in the Golgi. O-linked glycosylation occurs only in the Golgi. Answer: a) N-linked glycosylation.
2) Guess Question:
Which amino acid residue undergoes O-linked glycosylation?
a) Asparagine
b) Serine
c) Lysine
d) Histidine
Explanation: O-linked glycosylation occurs at serine or threonine residues in proteins. N-linked occurs at asparagine residues. This ensures proper folding, stability, and targeting of glycoproteins. Answer: b) Serine.
3) Guess Question:
A patient has defective N-acetylglucosaminyltransferase. Which process is impaired?
a) Protein glycosylation
b) Lipid metabolism
c) RNA splicing
d) Protein degradation
Explanation: N-acetylglucosaminyltransferase is crucial for N-linked glycosylation. Its deficiency impairs glycoprotein maturation, leading to congenital disorders of glycosylation. Answer: a) Protein glycosylation.
4) Guess Question:
Which organelle is responsible for protein sorting after glycosylation?
a) Nucleus
b) Lysosome
c) Golgi body
d) Mitochondria
Explanation: The Golgi apparatus is central to modifying glycoproteins and sorting them for secretion, lysosomal targeting, or membrane insertion. Answer: c) Golgi body.
5) Guess Question:
Which sugar is commonly attached in N-linked glycosylation?
a) Glucose
b) N-acetylglucosamine
c) Fucose
d) Galactose
Explanation: N-linked glycosylation begins with N-acetylglucosamine attached to asparagine, later extended with mannose, galactose, and fucose. Answer: b) N-acetylglucosamine.
6) Guess Question:
A patient with I-cell disease has defective:
a) Mannose-6-phosphate tagging
b) O-linked glycosylation
c) N-linked initiation
d) Ribosomal protein synthesis
Explanation: I-cell disease results from defective mannose-6-phosphate tagging in the Golgi, preventing lysosomal enzyme targeting. This leads to accumulation of substrates in lysosomes. Answer: a) Mannose-6-phosphate tagging.
7) Guess Question:
Which type of glycosylation occurs exclusively in the Golgi?
a) N-linked
b) O-linked
c) Both
d) None
Explanation: O-linked glycosylation occurs exclusively in the Golgi, involving sugars added to serine or threonine residues. N-linked begins in ER. Answer: b) O-linked.
8) Guess Question:
A patient presents with defective glycoprotein folding in ER. Likely accumulation is:
a) Unfolded proteins
b) Free glucose
c) Cholesterol
d) Lipids
Explanation: Defective glycosylation in the ER prevents proper folding of glycoproteins, leading to accumulation of unfolded proteins and activation of the unfolded protein response. Answer: a) Unfolded proteins.
9) Guess Question:
Which enzyme removes terminal mannose residues during glycosylation?
a) Mannosidase
b) Glycosyltransferase
c) Glucosidase
d) Kinase
Explanation: Mannosidases in the ER and Golgi remove mannose residues during N-linked glycosylation processing. This allows addition of other sugars. Answer: a) Mannosidase.
10) Guess Question:
In cystic fibrosis, defective glycosylation of CFTR affects:
a) Protein synthesis
b) Chloride channel trafficking
c) DNA repair
d) RNA stability
Explanation: CFTR protein misfolding due to defective glycosylation leads to impaired trafficking to the cell membrane, causing chloride transport defects in cystic fibrosis. Answer: b) Chloride channel trafficking.
Topic: Inborn Errors of Metabolism
Subtopic: Maple Syrup Urine Disease
Keyword Definitions:
• Maple Syrup Urine Disease (MSUD): Genetic disorder due to defect in branched-chain α-keto acid dehydrogenase complex.
• Type Ia MSUD: Subtype linked to mutation in E1α subunit gene (BCKDHA).
• Gene Mutation: Permanent alteration in DNA sequence affecting protein function.
• Branched-chain Amino Acids: Leucine, isoleucine, and valine metabolized via BCKD complex.
• Inheritance: MSUD is transmitted as an autosomal recessive condition.
• Leucine Toxicity: Excess leucine causes severe neurological dysfunction in MSUD.
• Tandem Mass Spectrometry: Diagnostic tool for detecting amino acid disorders in neonates.
• Thiamine: Cofactor of E1 activity in the BCKD complex.
• Burnt Sugar Odor: Characteristic maple syrup-like smell in urine of MSUD patients.
• Dialysis: Rapid detoxification method for metabolic crisis in MSUD.
Lead Question - 2013
In type Ia maple syrup urine disease, gene mutation seen is ?
a) E1α
b) E1β
c) E2
d) E3
Explanation: Type Ia MSUD results from mutation in the E1α subunit of branched-chain α-keto acid dehydrogenase, encoded by the BCKDHA gene.
This defect blocks oxidative decarboxylation of branched-chain amino acids, leading to accumulation and toxicity.
Therefore, the correct answer is a) E1α.
1) The enzyme complex defective in maple syrup urine disease is ?
a) Pyruvate dehydrogenase
b) Branched-chain α-keto acid dehydrogenase
c) Alpha-ketoglutarate dehydrogenase
d) Glucose-6-phosphatase
Explanation: MSUD occurs due to defective branched-chain α-keto acid dehydrogenase.
This enzyme normally metabolizes leucine, isoleucine, and valine.
When absent or deficient, these amino acids and their keto acids accumulate, producing neurotoxicity.
Clinical features include seizures and developmental delay.
Correct answer is b) Branched-chain α-keto acid dehydrogenase.
2) A 10-day-old neonate presents with vomiting, poor feeding, seizures, and urine with burnt sugar odor. Most likely diagnosis is ?
a) Phenylketonuria
b) Maple syrup urine disease
c) Alkaptonuria
d) Tyrosinemia
Explanation: A neonate with encephalopathy, seizures, poor feeding, and urine with burnt sugar odor is strongly suggestive of MSUD.
The disease presents in early life and may be fatal without rapid treatment.
Early diagnosis improves outcomes significantly.
Correct answer is b) Maple syrup urine disease.
3) Which branched-chain amino acid is most neurotoxic in maple syrup urine disease?
a) Leucine
b) Valine
c) Isoleucine
d) All equally toxic
Explanation: Although all branched-chain amino acids accumulate in MSUD, leucine is the most neurotoxic.
Elevated leucine levels cause cerebral edema, seizures, and brain damage.
Clinical management often focuses on rapid reduction of leucine concentration.
Therefore, the correct answer is a) Leucine.
4) A 6-month-old child with developmental delay is suspected of MSUD. Which confirmatory test is most appropriate?
a) Benedict’s test
b) Tandem mass spectrometry
c) Rothera’s test
d) Seliwanoff’s test
Explanation: Tandem mass spectrometry detects elevated plasma leucine, isoleucine, and valine levels, confirming MSUD.
It is also used in neonatal screening programs, ensuring early diagnosis and timely treatment.
This makes it the investigation of choice for suspected cases.
Correct answer is b) Tandem mass spectrometry.
5) Inheritance pattern of maple syrup urine disease is ?
a) Autosomal dominant
b) Autosomal recessive
c) X-linked dominant
d) Mitochondrial
Explanation: MSUD follows autosomal recessive inheritance, requiring mutations in both alleles for disease manifestation.
Parents are usually carriers without clinical features.
Risk of disease recurrence in siblings is 25% for carrier couples.
Correct answer is b) Autosomal recessive.
6) A neonate with MSUD develops acute encephalopathy. Immediate management includes ?
a) Vitamin C supplementation
b) Dialysis and intravenous glucose
c) High protein diet
d) Iron therapy
Explanation: Acute metabolic crises in MSUD are treated with dialysis to remove toxic metabolites and IV glucose to suppress catabolism.
This rapidly lowers amino acid levels and prevents further neurological injury.
Correct answer is b) Dialysis and intravenous glucose.
7) Which cofactor is essential for branched-chain α-keto acid dehydrogenase activity?
a) Thiamine pyrophosphate
b) Biotin
c) Vitamin C
d) Folic acid
Explanation: Branched-chain α-keto acid dehydrogenase requires several cofactors for function, including thiamine pyrophosphate, FAD, NAD+, and lipoic acid.
Thiamine is essential for E1 enzyme activity, and supplementation may benefit thiamine-responsive MSUD patients.
Correct answer is a) Thiamine pyrophosphate.
8) A 2-year-old child with intermittent ataxia and urine odor is diagnosed with intermittent MSUD. Which therapy may be beneficial?
a) Riboflavin
b) Thiamine
c) Pyridoxine
d) Vitamin K
Explanation: Intermittent MSUD cases may respond to high-dose thiamine supplementation, improving enzyme activity and reducing clinical episodes.
This response defines thiamine-responsive MSUD.
Correct answer is b) Thiamine.
9) A newborn screening program detects elevated leucine, isoleucine, and valine. Which disease should be suspected?
a) Alkaptonuria
b) Phenylketonuria
c) Maple syrup urine disease
d) Homocystinuria
Explanation: Detection of elevated branched-chain amino acids in newborn screening strongly suggests maple syrup urine disease.
Early detection allows initiation of dietary restriction, preventing irreversible neurological damage.
Correct answer is c) Maple syrup urine disease.
10) Dietary management of MSUD primarily involves restriction of ?
a) Methionine
b) Phenylalanine
c) Leucine, isoleucine, valine
d) Tyrosine
Explanation: The cornerstone of MSUD therapy is dietary restriction of branched-chain amino acids (leucine, isoleucine, valine).
Controlled supplementation ensures normal growth while avoiding toxic accumulation.
Careful monitoring is essential to maintain metabolic balance.
Correct answer is c) Leucine, isoleucine, valine.
Chapter: Molecular Biology
Topic: Gene Regulation
Subtopic: Sirtuins
Keyword Definitions:
• Sirtuins: A family of NAD⁺-dependent deacetylases regulating metabolism, aging, and stress response.
• Metabolism: The chemical processes by which cells generate energy and synthesize molecules.
• Memory: Brain process of storing and retrieving information.
• Vision: The sense that allows organisms to perceive light and images.
• Olfaction: The sensory system for detecting odors.
Lead Question - 2013
Sirtuins are associated with ?
a) Memory
b) Metabolism
c) Vision
d) Olfaction
Explanation: Sirtuins are NAD⁺-dependent enzymes involved in metabolism, aging, and stress adaptation. They regulate mitochondrial function, energy balance, DNA repair, and insulin sensitivity. Their role in promoting longevity is well established. The correct answer is Metabolism. Understanding sirtuins provides therapeutic implications in diabetes, neurodegeneration, and aging-related disorders.
1) Mutation in MSUD leads to deficiency of which enzyme?
a) Branched chain alpha-keto acid dehydrogenase
b) Pyruvate kinase
c) Glucose-6-phosphatase
d) Aldolase B
Explanation: Maple syrup urine disease (MSUD) results from mutations in the branched-chain alpha-keto acid dehydrogenase complex. This prevents breakdown of leucine, isoleucine, and valine, leading to neurotoxicity. The answer is Branched chain alpha-keto acid dehydrogenase. Early diagnosis and dietary management are essential for prevention of neurological complications.
2) A neonate with irritability, poor feeding, and sweet-smelling urine likely has defect in?
a) Urea cycle
b) Branched chain amino acid metabolism
c) Glycogenolysis
d) Fatty acid oxidation
Explanation: Clinical features of poor feeding, lethargy, seizures, and characteristic maple syrup odor in urine indicate MSUD. The underlying defect is in branched chain amino acid metabolism. Without treatment, it leads to severe neurological damage. Dietary restriction of branched-chain amino acids is the cornerstone of therapy.
3) Which vitamin-derived cofactor is essential for branched-chain ketoacid dehydrogenase complex?
a) Thiamine pyrophosphate
b) Pyridoxal phosphate
c) Biotin
d) Niacin
Explanation: The branched-chain ketoacid dehydrogenase requires several cofactors, including thiamine pyrophosphate, lipoic acid, FAD, NAD, and CoA. Thiamine deficiency worsens MSUD. The correct answer is Thiamine pyrophosphate. Some patients respond to high-dose thiamine therapy, known as thiamine-responsive MSUD.
4) A child with MSUD presents in metabolic crisis. Best immediate management is?
a) High protein diet
b) IV glucose with insulin
c) Branched chain amino acid supplementation
d) Ketogenic diet
Explanation: During metabolic crisis in MSUD, excess branched-chain amino acids accumulate, leading to encephalopathy. Immediate treatment includes IV glucose with insulin to reduce catabolism and promote protein synthesis. Dialysis may be required in severe cases. Long-term management involves dietary restriction of branched-chain amino acids.
5) Which metabolite accumulates in urine in MSUD, giving characteristic odor?
a) Homogentisic acid
b) Isovaleric acid
c) Alpha-ketoisocaproic acid
d) Phenylpyruvic acid
Explanation: In MSUD, alpha-ketoacids of branched chain amino acids accumulate, especially alpha-ketoisocaproic acid from leucine. This leads to neurotoxicity and distinctive maple syrup odor in urine. Early newborn screening by tandem mass spectrometry helps in timely detection and management.
6) Assertion-Reason: Assertion: Sirtuins promote longevity. Reason: They activate glycolysis and inhibit oxidative phosphorylation.
a) Both true, Reason correct explanation
b) Both true, Reason not explanation
c) Assertion true, Reason false
d) Both false
Explanation: Sirtuins are linked to longevity through improved DNA repair, stress resistance, and metabolic adaptation. They do not activate glycolysis but instead enhance mitochondrial oxidative metabolism. Thus, the Assertion is true, Reason is false. Calorie restriction upregulates sirtuins, contributing to lifespan extension.
7) Which sirtuin specifically regulates mitochondrial biogenesis?
a) SIRT1
b) SIRT2
c) SIRT3
d) SIRT6
Explanation: Sirtuins act at different cellular sites. SIRT1 activates PGC-1α, promoting mitochondrial biogenesis. SIRT3 acts within mitochondria, regulating enzymes of oxidative phosphorylation. This highlights their importance in energy metabolism and aging biology.
8) A patient with obesity and insulin resistance is found to have reduced sirtuin activity. This indicates disturbance in?
a) Glucose metabolism
b) Protein synthesis
c) Hemoglobin breakdown
d) Lipid absorption
Explanation: Sirtuins regulate insulin sensitivity, adipogenesis, and glucose-lipid metabolism. Reduced activity contributes to metabolic syndrome. Thus, the defect is in Glucose metabolism. Pharmacological activation of sirtuins (e.g., resveratrol) is being explored as therapy for diabetes and obesity.
9) Fill in the blank: In MSUD, the defective enzyme complex normally catalyzes __________.
a) Decarboxylation of branched chain alpha-keto acids
b) Carboxylation of pyruvate
c) Transamination of amino acids
d) Beta oxidation of fatty acids
Explanation: Branched chain alpha-keto acid dehydrogenase catalyzes decarboxylation of branched chain alpha-keto acids. Deficiency leads to accumulation of toxic intermediates in MSUD. This biochemical hallmark is used in newborn screening programs worldwide.
10) Choose the correct statements about sirtuins:
1. They are NAD⁺ dependent
2. They regulate stress responses
3. They inhibit apoptosis
4. They are DNA polymerases
a) 1,2,3 correct
b) 1,3,4 correct
c) 2,3,4 correct
d) 1,2,4 correct
Explanation: Sirtuins are NAD⁺ dependent enzymes that regulate metabolism, stress resistance, and apoptosis. They are not DNA polymerases. Thus, the correct option is 1,2,3. Their modulation is a therapeutic target in aging and metabolic disorders.
Chapter: Biochemistry
Topic: Enzymes
Subtopic: Cofactor Requirement of Phosphofructokinase
Keyword Definitions:
• Phosphofructokinase: A key glycolytic enzyme regulating conversion of fructose-6-phosphate to fructose-1,6-bisphosphate.
• Cofactor: A non-protein molecule essential for enzyme activity.
• Magnesium: A divalent cation required by many kinases for stabilization of ATP.
• Inorganic phosphate: A component of phosphorylated intermediates in metabolism.
• Manganese: A trace element acting as cofactor for some hydrolases and ligases.
• Copper: A trace element crucial for enzymes like cytochrome c oxidase.
Lead Question - 2013
Which element is required by phosphofructokinase?
a) Magnesium
b) Inorganic phosphate
c) Manganese
d) Copper
Explanation: Phosphofructokinase, a rate-limiting enzyme in glycolysis, requires magnesium as a cofactor. Magnesium binds to ATP, stabilizing its negative charges, enabling phosphate transfer. This regulation ensures controlled glycolytic flux. Without magnesium, ATP cannot function efficiently as a phosphate donor in kinase-mediated reactions.
1) Which step of glycolysis is catalyzed by phosphofructokinase?
a) Glucose to glucose-6-phosphate
b) Fructose-6-phosphate to fructose-1,6-bisphosphate
c) 1,3-Bisphosphoglycerate to 3-phosphoglycerate
d) Phosphoenolpyruvate to pyruvate
Explanation: Phosphofructokinase catalyzes the irreversible phosphorylation of fructose-6-phosphate to fructose-1,6-bisphosphate, a committed step of glycolysis. This makes it a key regulatory enzyme. It is allosterically regulated by ATP, citrate, and AMP, reflecting cellular energy status and balancing glycolytic flux with energy requirements.
2) A patient presents with muscle cramps and exercise intolerance due to phosphofructokinase deficiency. This condition is called?
a) McArdle disease
b) Tarui disease
c) Von Gierke disease
d) Pompe disease
Explanation: Deficiency of phosphofructokinase in muscle causes Tarui disease (Glycogen storage disease type VII). Patients exhibit exercise intolerance, muscle cramps, and myoglobinuria. It impairs glycolysis and energy production in skeletal muscles, leading to clinical symptoms especially during physical exertion.
3) Phosphofructokinase is allosterically inhibited by?
a) AMP
b) ATP
c) Fructose-2,6-bisphosphate
d) ADP
Explanation: ATP serves both as substrate and allosteric inhibitor of phosphofructokinase. High ATP levels signal sufficient energy, downregulating glycolysis. Thus, the correct answer is ATP. Conversely, AMP and fructose-2,6-bisphosphate activate the enzyme, enhancing glycolytic flux during energy demand.
4) A neonate with lactic acidosis, muscle weakness, and positive family history likely has deficiency of?
a) Phosphofructokinase
b) Pyruvate dehydrogenase
c) Glucose-6-phosphatase
d) Carnitine acyltransferase
Explanation: Lactic acidosis with muscle weakness and glycolytic block suggests phosphofructokinase deficiency. The defect impairs energy production from glucose metabolism, especially during exercise. Tarui disease, a rare autosomal recessive disorder, represents this deficiency. Early recognition helps in dietary and lifestyle modifications for management.
5) Which molecule strongly activates phosphofructokinase in liver?
a) Fructose-2,6-bisphosphate
b) ATP
c) Citrate
d) NADH
Explanation: Fructose-2,6-bisphosphate is the most potent activator of phosphofructokinase in liver. It overrides ATP inhibition and ensures glycolysis proceeds during fed state. Hormonal regulation via insulin increases fructose-2,6-bisphosphate, linking enzyme activity with metabolic state and glucose utilization.
6) Assertion-Reason: Assertion: Magnesium is required for phosphofructokinase activity. Reason: It stabilizes the phosphate groups of ATP.
a) Both true, Reason correct explanation
b) Both true, Reason not explanation
c) Assertion true, Reason false
d) Both false
Explanation: Kinases, including phosphofructokinase, require magnesium to stabilize ATP’s negative charges and facilitate phosphate transfer. Hence both assertion and reason are true, with the reason being the correct explanation. The correct option is a. This exemplifies the vital biochemical role of divalent cations in enzymatic catalysis.
7) In Tarui disease, which biochemical pathway is primarily affected?
a) Glycolysis
b) Gluconeogenesis
c) Glycogenolysis
d) Pentose phosphate pathway
Explanation: Tarui disease is a deficiency of phosphofructokinase, impairing glycolysis. This reduces ATP production in muscle, leading to exercise-induced cramps and myoglobinuria. Glycogen accumulates due to blocked glycolysis, despite normal glycogenolysis. Thus, the principal metabolic block is glycolytic pathway.
8) A 5-year-old child develops muscle cramps after mild exertion. Blood lactate fails to rise after exercise. The defective enzyme is?
a) Phosphofructokinase
b) Lactate dehydrogenase
c) Glucose-6-phosphate dehydrogenase
d) Pyruvate kinase
Explanation: In exercise testing, absence of lactate rise suggests impaired glycolysis upstream of pyruvate. Phosphofructokinase deficiency prevents glycolytic flux, thus lactate does not accumulate. This clinical scenario describes Tarui disease, a glycogen storage disorder affecting skeletal muscle glycolysis.
9) Fill in the blank: Phosphofructokinase acts as the __________ of glycolysis.
a) Substrate
b) Rate-limiting enzyme
c) Transporter
d) Product
Explanation: Phosphofructokinase is the rate-limiting enzyme of glycolysis. Its irreversible step commits glucose towards energy production. Regulation by ATP, citrate, AMP, and fructose-2,6-bisphosphate balances glycolysis according to energy needs. This central role makes it a critical control point of glucose metabolism.
10) Choose the correct statements about phosphofructokinase:
1. It requires magnesium as a cofactor
2. It is inhibited by high ATP
3. It catalyzes reversible reaction
4. It is the committed step of glycolysis
a) 1,2,4 correct
b) 1,3,4 correct
c) 2,3,4 correct
d) 1,2,3 correct
Explanation: Phosphofructokinase requires magnesium, is inhibited by ATP, and catalyzes the committed step of glycolysis. Its reaction is irreversible. Therefore, the correct option is 1,2,4. This highlights its role as the central regulator of glucose catabolism and energy balance in cells.
Chapter: Biochemistry
Topic: Enzymes
Subtopic: Metalloenzymes
Keyword Definitions:
• Carboxypeptidase: A proteolytic enzyme that hydrolyzes the terminal peptide bond at the carboxyl end of proteins.
• Metalloenzyme: Enzyme requiring a metal ion for catalytic activity.
• Zinc: An essential trace element functioning as a cofactor in many hydrolases and peptidases.
• Copper: A metal cofactor used in oxidative enzymes.
• Iron: A transition metal required in oxygen transport and redox enzymes.
Lead Question - 2013
Carboxypeptidase contains which mineral?
a) Copper
b) Zinc
c) Iron
d) None
Explanation: Carboxypeptidase is a zinc-containing metalloenzyme that cleaves amino acids from the carboxyl end of polypeptides. Zinc stabilizes the enzyme structure and directly participates in catalysis. Its presence is essential for peptide bond hydrolysis. Hence, the correct answer is b) Zinc.
1) Carboxypeptidase acts on which terminal of polypeptides?
a) Amino terminal
b) Carboxyl terminal
c) Internal bonds
d) Nucleic acids
Explanation: Carboxypeptidase specifically hydrolyzes amino acids from the carboxyl terminal of polypeptides. It complements aminopeptidase, which acts on the amino terminal. Together, these enzymes help in complete protein digestion. The correct answer is b) Carboxyl terminal.
2) A child with zinc deficiency presents with poor wound healing, growth retardation, and impaired taste sensation. Which enzyme activity is also impaired?
a) Carboxypeptidase
b) Catalase
c) Cytochrome oxidase
d) Peroxidase
Explanation: Zinc deficiency impairs several enzymes, notably carboxypeptidase, leading to defective protein digestion. This contributes to poor growth, delayed wound healing, and hypogeusia. Zinc supplementation restores enzyme activity. Correct answer is a) Carboxypeptidase.
3) Which metal is required for carbonic anhydrase activity?
a) Copper
b) Zinc
c) Magnesium
d) Iron
Explanation: Like carboxypeptidase, carbonic anhydrase also requires zinc for catalysis. Zinc stabilizes water molecules, enabling rapid hydration of carbon dioxide. This highlights the central biochemical role of zinc in metalloenzymes. Correct answer is b) Zinc.
4) A patient with chronic pancreatitis shows impaired protein digestion. Which pancreatic zinc enzyme is most likely affected?
a) Carboxypeptidase
b) Pepsin
c) Trypsin
d) Rennin
Explanation: Carboxypeptidase, secreted by the pancreas, is a zinc-dependent protease. In chronic pancreatitis, enzyme secretion decreases, impairing terminal digestion of peptides. Clinical features include malabsorption and steatorrhea. Thus, carboxypeptidase is primarily affected. Correct answer is a) Carboxypeptidase.
5) Which vitamin deficiency worsens zinc absorption and thereby carboxypeptidase activity?
a) Vitamin C
b) Vitamin D
c) Vitamin B6
d) Vitamin A
Explanation: Vitamin B6 deficiency may worsen zinc metabolism and impair enzyme activity, including carboxypeptidase. This leads to metabolic imbalance and defective protein digestion. The correct answer is c) Vitamin B6.
6) Assertion-Reason: Assertion: Carboxypeptidase requires zinc for activity. Reason: Zinc helps stabilize enzyme conformation and participates in catalysis.
a) Both true, Reason correct explanation
b) Both true, Reason not explanation
c) Assertion true, Reason false
d) Both false
Explanation: Carboxypeptidase requires zinc, which directly stabilizes the enzyme and facilitates peptide bond hydrolysis. Thus, both assertion and reason are true, and reason correctly explains the assertion. Correct answer is a.
7) A neonate with congenital zinc malabsorption presents with dermatitis and diarrhea. Which pancreatic enzyme deficiency aggravates protein maldigestion?
a) Carboxypeptidase
b) Amylase
c) Lipase
d) Maltase
Explanation: Zinc malabsorption impairs metalloenzymes like carboxypeptidase, reducing protein digestion efficiency. Clinical signs include dermatitis, diarrhea, and poor growth. Thus, impaired carboxypeptidase activity worsens nutritional deficiency in affected neonates. Correct answer is a) Carboxypeptidase.
8) Which of the following enzymes is zinc-dependent?
a) Carboxypeptidase
b) Carbonic anhydrase
c) Alcohol dehydrogenase
d) All of the above
Explanation: Zinc is a common cofactor for many enzymes, including carboxypeptidase, carbonic anhydrase, and alcohol dehydrogenase. It stabilizes enzyme structure and facilitates catalysis. Hence, the correct option is d) All of the above.
9) Fill in the blank: Carboxypeptidase is secreted by the __________.
a) Liver
b) Stomach
c) Pancreas
d) Intestine
Explanation: Carboxypeptidase is secreted by the pancreas as an inactive proenzyme, activated in the intestine. It aids terminal protein digestion. Hence, the correct answer is c) Pancreas.
10) Choose the correct statements regarding carboxypeptidase:
1. It is a metalloenzyme
2. It requires zinc
3. It acts on amino terminal
4. It is secreted by pancreas
a) 1,2,4 correct
b) 1,3,4 correct
c) 2,3,4 correct
d) 1,2,3 correct
Explanation: Carboxypeptidase is a zinc-dependent metalloenzyme secreted by the pancreas and acts on the carboxyl terminal. Correct statements are 1,2,4. The correct option is a) 1,2,4 correct.
Chapter: Biochemistry
Topic: Enzyme Kinetics
Subtopic: Enzyme Specificity
Keyword Definitions:
• Enzyme specificity: The ability of an enzyme to select a particular substrate among similar molecules.
• Km (Michaelis constant): Substrate concentration at which reaction velocity is half of Vmax.
• Vmax: Maximum velocity of an enzymatic reaction at saturating substrate concentration.
• Turnover number: Number of substrate molecules converted per enzyme molecule per second.
Lead Question - 2013
Enzyme specificity is given by ?
a) Km
b) Vmax
c) Both
d) None
Explanation: Enzyme specificity refers to how selectively an enzyme binds its substrate. Both Km and Vmax contribute: Km reflects affinity, while Vmax indicates catalytic efficiency. Combined, they define the enzyme’s specificity constant, kcat/Km, representing substrate selection and conversion rate. Correct answer is c) Both.
1) Which parameter defines the affinity of enzyme for substrate?
a) Km
b) Vmax
c) Kcat
d) pH optimum
Explanation: Km represents the substrate concentration at which enzyme reaches half-maximal velocity. Lower Km indicates higher affinity. This allows prediction of substrate binding efficiency. Vmax and kcat describe catalytic turnover, but affinity is uniquely determined by Km. Correct answer is a) Km.
2) Clinical scenario: A patient presents with enzyme deficiency causing decreased catalytic efficiency. Which parameter reflects this defect?
a) Km
b) Vmax
c) Both
d) None
Explanation: Reduced enzymatic activity is reflected in Vmax, the maximum rate of product formation. Km may remain unchanged if substrate binding is unaffected. Vmax decrease indicates lower enzyme concentration or turnover. Correct answer is b) Vmax.
3) Turnover number (kcat) represents:
a) Enzyme affinity
b) Catalytic efficiency
c) Substrate inhibition
d) Substrate concentration
Explanation: kcat is the number of substrate molecules converted to product per enzyme molecule per second under saturating substrate conditions. It reflects catalytic efficiency independent of substrate affinity. Correct answer is b) Catalytic efficiency.
4) A patient has a mutant enzyme with same Km but decreased Vmax. Which property is affected?
a) Affinity
b) Catalytic turnover
c) Substrate specificity
d) pH optimum
Explanation: Unchanged Km indicates normal substrate binding (affinity intact). Decreased Vmax indicates reduced catalytic turnover. The enzyme binds substrate normally but converts it slower. Correct answer is b) Catalytic turnover.
5) Which parameter is used to calculate specificity constant?
a) Km only
b) Vmax only
c) kcat/Km
d) Turnover number only
Explanation: Specificity constant is kcat/Km, combining catalytic efficiency (kcat) and substrate affinity (Km). Higher kcat/Km indicates higher specificity. It allows comparison of enzymes or mutants for substrate preference. Correct answer is c) kcat/Km.
6) Assertion-Reason: Assertion: Enzyme specificity is determined by Km. Reason: Km reflects enzyme’s substrate affinity.
a) Both true, Reason correct
b) Both true, Reason incorrect
c) Assertion true, Reason false
d) Both false
Explanation: Km indeed indicates substrate affinity, a component of enzyme specificity. However, Vmax also contributes to overall specificity. Therefore, assertion is partially correct, but alone it does not fully define specificity. Correct answer is b) Both true, Reason not explanation.
7) A neonate with a metabolic enzyme mutation shows normal binding but slower product formation. Which kinetic parameter is mainly affected?
a) Km
b) Vmax
c) kcat/Km
d) Substrate concentration
Explanation: Normal binding implies Km is unchanged. Slow product formation reflects reduced Vmax or kcat. This indicates catalytic turnover defect, often seen in inherited enzyme deficiencies. Correct answer is b) Vmax.
8) Which factor increases enzyme specificity constant?
a) High kcat, low Km
b) Low kcat, high Km
c) High Km only
d) Low kcat only
Explanation: The specificity constant (kcat/Km) increases with high kcat (fast turnover) and low Km (high affinity). This maximizes enzymatic efficiency and substrate selection. Correct answer is a) High kcat, low Km.
9) Fill in the blank: Enzyme specificity can be quantitatively expressed as __________.
a) kcat
b) Km
c) kcat/Km
d) Vmax
Explanation: Enzyme specificity combines affinity and catalytic rate, expressed quantitatively as kcat/Km. High values indicate high efficiency and selective substrate conversion. This metric is essential for comparing enzyme-substrate interactions and evaluating mutants. Correct answer is c) kcat/Km.
10) Choose the correct statements regarding enzyme specificity:
1. Km reflects substrate affinity
2. Vmax reflects catalytic turnover
3. Specificity constant is kcat/Km
4. Specificity depends only on Km
a) 1,2,3 correct
b) 1,3,4 correct
c) 2,3,4 correct
d) 1,2,4 correct
Explanation: Enzyme specificity is determined by both substrate affinity and catalytic rate. Km reflects affinity, Vmax and kcat reflect turnover, and kcat/Km gives the specificity constant. Statement 4 is incorrect. Correct answer is a) 1,2,3 correct.
Chapter: Biochemistry
Topic: Enzyme Kinetics
Subtopic: Catalytic Efficiency
Keyword Definitions:
• kcat: Turnover number; number of substrate molecules converted per enzyme per second.
• Km: Michaelis constant; substrate concentration at half-maximal velocity.
• kcat/Km: Specificity constant; measures enzyme efficiency combining substrate affinity and catalytic rate.
• Enzyme efficiency: Overall capacity of an enzyme to convert substrate to product.
• Turnover number: Same as kcat; rate of catalysis per enzyme molecule.
Lead Question - 2013
kcat/Km is a measure of -
a) Enzyme efficiency
b) Speed of enzymatic reaction
c) Concentration of substrate
d) Enzyme turnover
Explanation: The ratio kcat/Km is called the specificity constant and quantitatively represents enzyme efficiency. It accounts for both substrate affinity (Km) and catalytic rate (kcat), providing a comprehensive measure of how efficiently an enzyme converts substrate to product under physiological conditions. Correct answer is a) Enzyme efficiency.
1) Which parameter defines enzyme turnover?
a) kcat
b) Km
c) Vmax
d) kcat/Km
Explanation: kcat, the turnover number, is the number of substrate molecules converted per enzyme molecule per second. It represents the catalytic activity independent of substrate concentration, reflecting the intrinsic enzymatic capability. Correct answer is a) kcat.
2) A patient presents with metabolic enzyme mutation causing slow product formation but normal substrate binding. Which parameter is reduced?
a) Km
b) Vmax
c) kcat
d) kcat/Km
Explanation: Normal substrate binding (Km normal) with slower product formation indicates a decrease in kcat or Vmax. kcat reduction shows reduced catalytic turnover per enzyme molecule. This reflects impaired enzyme efficiency and can be seen in inherited enzyme deficiencies. Correct answer is c) kcat.
3) Which factor is used to compare catalytic efficiency of two enzymes?
a) Km
b) Vmax
c) kcat/Km
d) Turnover number only
Explanation: kcat/Km combines substrate affinity (Km) and catalytic rate (kcat) to evaluate enzyme efficiency. It allows direct comparison between enzymes or mutants. Higher kcat/Km indicates greater efficiency in converting substrate to product. Correct answer is c) kcat/Km.
4) Clinical scenario: A child with enzyme deficiency has low kcat/Km. What is the consequence?
a) Normal substrate metabolism
b) Decreased enzymatic efficiency
c) Increased product formation
d) Increased turnover
Explanation: Low kcat/Km reflects reduced enzyme efficiency, causing slower substrate conversion and accumulation of intermediates. This is clinically significant in inborn errors of metabolism where enzymatic defects impair physiological processes. Correct answer is b) Decreased enzymatic efficiency.
5) What does a high kcat/Km indicate?
a) Poor enzyme-substrate affinity
b) High catalytic efficiency
c) Slow enzyme reaction
d) Low substrate turnover
Explanation: High kcat/Km signifies high enzyme efficiency: strong substrate affinity (low Km) and rapid turnover (high kcat). It means the enzyme rapidly converts substrate to product even at low substrate concentrations. Correct answer is b) High catalytic efficiency.
6) Assertion-Reason: Assertion: kcat/Km is a measure of enzyme efficiency. Reason: It combines substrate affinity and catalytic rate.
a) Both true, Reason correct
b) Both true, Reason not explanation
c) Assertion true, Reason false
d) Both false
Explanation: kcat/Km integrates substrate binding (Km) and turnover number (kcat) into a single measure of efficiency. This quantifies how effectively an enzyme converts substrate to product under physiological conditions. Therefore, both assertion and reason are true, and reason correctly explains the assertion. Correct answer is a.
7) A neonate with metabolic disorder shows low kcat/Km but normal Km. Which property is defective?
a) Substrate binding
b) Catalytic turnover
c) Enzyme concentration
d) Allosteric regulation
Explanation: Normal Km indicates intact substrate binding, while low kcat/Km reflects reduced catalytic turnover. The enzyme binds substrate properly but converts it slower, characteristic of certain metabolic enzyme deficiencies. Correct answer is b) Catalytic turnover.
8) Fill in the blank: kcat/Km is also called __________.
a) Turnover number
b) Specificity constant
c) Michaelis constant
d) Catalytic rate
Explanation: kcat/Km is termed the specificity constant. It measures enzymatic efficiency and substrate selectivity. High values indicate fast turnover and strong affinity, essential in comparing enzymes or assessing mutations. Correct answer is b) Specificity constant.
9) Which factor is independent of substrate concentration?
a) Km
b) Vmax
c) kcat
d) Reaction velocity at low substrate
Explanation: kcat is intrinsic to the enzyme and independent of substrate concentration. It represents the maximum number of substrate molecules converted per enzyme per second at saturating substrate. Correct answer is c) kcat.
10) Choose the correct statements regarding kcat/Km:
1. Represents enzyme efficiency
2. High value indicates strong substrate affinity
3. Combines kcat and Km
4. Depends only on substrate concentration
a) 1,2,3 correct
b) 1,3,4 correct
c) 2,3,4 correct
d) 1,2,4 correct
Explanation: kcat/Km quantifies enzyme efficiency by combining kcat (turnover) and Km (affinity). High values reflect strong substrate binding and fast conversion. It is independent of substrate concentration. Correct statements are 1,2,3. Correct answer is a) 1,2,3 correct.
Chapter: Biochemistry
Topic: Enzyme Kinetics
Subtopic: Enzyme Turnover Number
Keyword Definitions:
• Enzyme turnover number (kcat): Number of substrate molecules converted per enzyme molecule per second.
• Q10 coefficient: Rate increase of an enzymatic reaction when temperature rises by 10°C.
• Temperature effect on enzymes: Reaction rates generally increase with temperature up to an optimum point.
• Activation energy: Energy required for a chemical reaction to proceed.
• Reaction velocity: Speed at which substrate converts to product under given conditions.
Lead Question - 2013
Q10 in enzyme matches with ?
a) 2
b) 4
c) 8
d) 10
Explanation: The Q10 value describes how enzyme reaction velocity changes with a 10°C increase in temperature. Most enzymes show a Q10 of approximately 2, meaning the reaction rate doubles. Extreme temperatures denature enzymes, reducing activity. Correct answer is a) 2.
1) What does Q10 represent in enzyme kinetics?
a) Enzyme turnover number
b) Temperature coefficient
c) Michaelis constant
d) Reaction velocity
Explanation: Q10 is the temperature coefficient, showing the factor by which reaction rate increases when temperature rises by 10°C. It quantifies thermal sensitivity of enzymes, generally ranging between 2–3 for most biological enzymes. Correct answer is b) Temperature coefficient.
2) A patient has a metabolic disorder where enzyme activity increases excessively with fever. Which kinetic concept explains this?
a) Km
b) Vmax
c) Q10
d) kcat
Explanation: Increased enzymatic activity with temperature changes is explained by Q10. The Q10 value predicts how much reaction velocity increases with a 10°C temperature rise. Excessive activity may impact metabolic balance. Correct answer is c) Q10.
3) If enzyme Q10 is 2, how does reaction rate change when temperature rises from 20°C to 30°C?
a) Doubles
b) Triples
c) No change
d) Halves
Explanation: A Q10 of 2 means reaction rate doubles for each 10°C increase. Therefore, raising temperature from 20°C to 30°C doubles the enzyme activity, assuming the enzyme remains stable and not denatured. Correct answer is a) Doubles.
4) Which factor can reduce Q10 of an enzyme?
a) Denaturation
b) Saturating substrate
c) Coenzyme availability
d) None
Explanation: Denaturation at high temperatures reduces enzyme activity and Q10, as the protein loses structure and catalytic ability. Substrate saturation or coenzyme presence affects velocity but not Q10 directly. Correct answer is a) Denaturation.
5) Which Q10 value is typical for most physiological enzymes?
a) 1
b) 2
c) 5
d) 10
Explanation: Most physiological enzymes have a Q10 between 2–3, meaning reaction rate doubles or slightly more for every 10°C temperature increase. Extreme deviations indicate abnormal thermal sensitivity or enzyme dysfunction. Correct answer is b) 2.
6) Assertion-Reason: Assertion: Q10 predicts temperature effect on enzyme rate. Reason: Reaction velocity doubles with every 10°C increase for all enzymes.
a) Both true, Reason correct
b) Both true, Reason not explanation
c) Assertion true, Reason false
d) Both false
Explanation: Q10 predicts temperature effect, but doubling per 10°C is typical, not universal. Hence, assertion is correct, but reason is not universally true. Correct answer is b) Both true, Reason not explanation.
7) A febrile neonate shows exaggerated enzyme reactions. Which parameter is useful for predicting reaction change with fever?
a) Km
b) Vmax
c) Q10
d) kcat
Explanation: Q10 is the temperature coefficient used to predict enzyme reaction changes with temperature variations, such as fever. It helps anticipate metabolic shifts and potential accumulation of intermediates. Correct answer is c) Q10.
8) Fill in the blank: The Q10 value measures the __________ of enzymatic reaction with temperature.
a) Affinity
b) Rate increase
c) Km
d) Turnover number
Explanation: Q10 quantifies the rate increase of enzyme-catalyzed reactions for a 10°C temperature rise. It provides insight into thermal sensitivity and physiological adaptation. Correct answer is b) Rate increase.
9) Which factor does not affect Q10 significantly?
a) Substrate saturation
b) Temperature rise
c) Enzyme denaturation
d) pH extremes
Explanation: Substrate saturation affects reaction velocity but not Q10, which is specifically the temperature coefficient. Temperature, denaturation, and pH extremes influence enzyme stability and Q10. Correct answer is a) Substrate saturation.
10) Choose correct statements regarding Q10:
1. Measures temperature sensitivity
2. Typical value ~2 for physiological enzymes
3. Predicts exact rate change for all enzymes
4. Not affected by denaturation
a) 1,2 correct
b) 1,3 correct
c) 2,3,4 correct
d) 1,2,4 correct
Explanation: Q10 measures temperature sensitivity, with typical physiological value around 2. It cannot predict exact rate changes universally, and denaturation can lower Q10. Therefore, correct statements are 1 and 2. Correct answer is a) 1,2 correct.
Chapter: Biochemistry
Topic: Enzymes
Subtopic: Enzyme Classification
Keyword Definitions:
• Lyase: Enzyme that cleaves bonds without hydrolysis or oxidation, often forming double bonds or rings.
• Decarboxylase: A type of lyase that removes a carboxyl group releasing CO2.
• Synthetase: Enzyme that forms bonds using energy from nucleoside triphosphates.
• Kinase: Enzyme transferring phosphate groups from ATP to substrates.
• Oxygenase: Enzyme incorporating oxygen into substrates.
Lead Question - 2013
Which of the following is a lyase ?
a) Decarboxylase
b) Synthetase
c) Kinase
d) Oxygenase
Explanation: Decarboxylase is a classic lyase, removing a carboxyl group from substrates without hydrolysis or oxidation, producing CO2 and a new compound. Synthetases use ATP, kinases transfer phosphate, and oxygenases incorporate oxygen. Therefore, the correct answer is a) Decarboxylase.
1) Which enzyme class cleaves C-C, C-O, or C-N bonds without hydrolysis?
a) Lyase
b) Hydrolase
c) Oxidoreductase
d) Transferase
Explanation: Lyases cleave chemical bonds without water (hydrolysis) or oxidation, often forming double bonds. Hydrolases use water, oxidoreductases catalyze redox reactions, and transferases transfer functional groups. Correct answer is a) Lyase.
2) A neonate presents with accumulation of pyruvate due to defective decarboxylase. Which enzyme type is affected?
a) Lyase
b) Hydrolase
c) Transferase
d) Oxidoreductase
Explanation: Decarboxylases are lyases, removing carboxyl groups from substrates like pyruvate. Deficiency causes accumulation and metabolic disturbances in neonates. Correct identification of enzyme class is crucial for diagnosis. Correct answer is a) Lyase.
3) Which enzyme catalyzes cleavage of C-C bond in pyruvate?
a) Pyruvate decarboxylase
b) Pyruvate kinase
c) Pyruvate synthetase
d) Pyruvate oxidase
Explanation: Pyruvate decarboxylase is a lyase that cleaves the C-C bond, releasing CO2. Kinase transfers phosphate, synthetase forms bonds using ATP, and oxidase incorporates oxygen. Correct answer is a) Pyruvate decarboxylase.
4) Which enzyme converts fumarate to malate?
a) Fumarase
b) Succinate dehydrogenase
c) Malate synthase
d) Pyruvate carboxylase
Explanation: Fumarase is a lyase that hydrates fumarate to form malate, cleaving C=C bonds with addition of water. Other enzymes have different functions in the citric acid cycle. Correct answer is a) Fumarase.
5) A patient has a genetic defect in alanine decarboxylase. Which enzyme class is involved?
a) Lyase
b) Hydrolase
c) Ligase
d) Transferase
Explanation: Alanine decarboxylase is a lyase, removing the carboxyl group from alanine. Mutation affects amino acid metabolism, causing clinical symptoms. Correct answer is a) Lyase.
6) Assertion-Reason: Assertion: Decarboxylase is a lyase. Reason: Lyases catalyze bond cleavage without hydrolysis or oxidation.
a) Both true, Reason correct
b) Both true, Reason not explanation
c) Assertion true, Reason false
d) Both false
Explanation: Decarboxylase removes a carboxyl group without hydrolysis or oxidation, fitting the definition of a lyase. Therefore, both assertion and reason are true, and reason correctly explains assertion. Correct answer is a) Both true, Reason correct.
7) Clinical scenario: Accumulation of CO2 occurs due to defective pyruvate decarboxylase. Which enzyme class is responsible?
a) Lyase
b) Ligase
c) Hydrolase
d) Transferase
Explanation: Pyruvate decarboxylase is a lyase that removes CO2 from pyruvate. Deficiency causes metabolic disturbances like lactic acidosis. Recognizing the enzyme class aids in proper diagnosis and management. Correct answer is a) Lyase.
8) Fill in the blank: Fumarase belongs to __________ class of enzymes.
a) Lyase
b) Hydrolase
c) Transferase
d) Oxidoreductase
Explanation: Fumarase catalyzes hydration of fumarate to malate, cleaving double bonds without hydrolysis, making it a classic lyase. Correct answer is a) Lyase.
9) Which enzyme removes carboxyl groups releasing CO2?
a) Decarboxylase
b) Kinase
c) Ligase
d) Oxygenase
Explanation: Decarboxylase removes carboxyl groups, generating CO2. This reaction is characteristic of lyases, essential in metabolic pathways such as glycolysis and amino acid degradation. Correct answer is a) Decarboxylase.
10) Choose correct statements regarding lyases:
1. Cleave bonds without hydrolysis
2. Include decarboxylases and fumarase
3. Require ATP
4. Can form double bonds or rings
a) 1,2,4 correct
b) 1,2 correct
c) 2,3 correct
d) 1,3,4 correct
Explanation: Lyases cleave bonds without hydrolysis, include decarboxylases and fumarase, and often form double bonds or rings. They do not require ATP. Correct statements are 1,2,4. Correct answer is a) 1,2,4 correct.