Q.1 Which of the following is the primary energy currency of the cell?
ATP
GTP
NADH
FADH2
Explanation - ATP (adenosine triphosphate) is the universal energy currency in cells, storing and transferring energy for various biochemical reactions.
Correct answer is: ATP
Q.2 Which enzyme is considered the rate-limiting step of glycolysis?
Hexokinase
Phosphofructokinase-1
Pyruvate kinase
Aldolase
Explanation - Phosphofructokinase-1 (PFK-1) catalyzes the conversion of fructose-6-phosphate to fructose-1,6-bisphosphate and is the key regulatory step of glycolysis.
Correct answer is: Phosphofructokinase-1
Q.3 In the absence of oxygen, pyruvate is converted into:
Acetyl-CoA
Lactate
Citrate
Oxaloacetate
Explanation - Under anaerobic conditions, pyruvate is reduced to lactate by lactate dehydrogenase to regenerate NAD+, allowing glycolysis to continue.
Correct answer is: Lactate
Q.4 Which organ is the main site of gluconeogenesis?
Muscle
Liver
Kidney
Adipose tissue
Explanation - The liver is the primary site of gluconeogenesis, producing glucose during fasting to maintain blood glucose levels.
Correct answer is: Liver
Q.5 Which molecule links glycolysis and the TCA cycle?
Pyruvate
Acetyl-CoA
Oxaloacetate
Citrate
Explanation - Pyruvate is converted into Acetyl-CoA by pyruvate dehydrogenase, linking glycolysis with the TCA cycle.
Correct answer is: Acetyl-CoA
Q.6 Which of the following is a product of the pentose phosphate pathway?
ATP
NADPH
FADH2
Pyruvate
Explanation - The pentose phosphate pathway generates NADPH and ribose-5-phosphate, essential for reductive biosynthesis and nucleotide synthesis.
Correct answer is: NADPH
Q.7 Which enzyme deficiency causes glycogen storage disease type I (Von Gierke’s disease)?
Glucose-6-phosphatase
Debranching enzyme
Glycogen phosphorylase
Branching enzyme
Explanation - Von Gierke’s disease is due to a deficiency of glucose-6-phosphatase, leading to severe fasting hypoglycemia.
Correct answer is: Glucose-6-phosphatase
Q.8 Which vitamin is required for the carboxylation reactions in metabolism?
Vitamin B12
Vitamin B6
Biotin
Niacin
Explanation - Biotin acts as a coenzyme for carboxylase enzymes that catalyze CO2 fixation reactions in metabolism.
Correct answer is: Biotin
Q.9 Which step in the TCA cycle produces GTP?
Citrate to isocitrate
Succinyl-CoA to succinate
Malate to oxaloacetate
α-Ketoglutarate to succinyl-CoA
Explanation - The conversion of succinyl-CoA to succinate by succinyl-CoA synthetase generates GTP via substrate-level phosphorylation.
Correct answer is: Succinyl-CoA to succinate
Q.10 Which process occurs in the mitochondrial matrix?
Glycolysis
Fatty acid synthesis
TCA cycle
Pentose phosphate pathway
Explanation - The TCA cycle occurs in the mitochondrial matrix, where acetyl-CoA is oxidized to CO2, producing NADH and FADH2.
Correct answer is: TCA cycle
Q.11 What is the main storage form of carbohydrates in humans?
Glucose
Glycogen
Starch
Cellulose
Explanation - Humans store carbohydrates as glycogen, primarily in the liver and skeletal muscle.
Correct answer is: Glycogen
Q.12 Which hormone stimulates glycogen breakdown in the liver?
Insulin
Glucagon
Cortisol
Thyroxine
Explanation - Glucagon activates glycogen phosphorylase via cAMP signaling to break down glycogen and release glucose.
Correct answer is: Glucagon
Q.13 The Cori cycle involves the cycling of:
Glucose and lactate
Glucose and alanine
Glucose and pyruvate
Fatty acids and ketones
Explanation - In the Cori cycle, lactate from anaerobic glycolysis in muscles is transported to the liver, converted to glucose, and returned to muscles.
Correct answer is: Glucose and lactate
Q.14 Which of the following is the main ketone body produced during fasting?
Acetoacetate
Pyruvate
Acetone
Citrate
Explanation - Acetoacetate and β-hydroxybutyrate are the main ketone bodies produced in the liver during fasting or starvation.
Correct answer is: Acetoacetate
Q.15 Which enzyme is inhibited by malonate, a competitive inhibitor?
Citrate synthase
Succinate dehydrogenase
Isocitrate dehydrogenase
Pyruvate kinase
Explanation - Malonate structurally resembles succinate and competitively inhibits succinate dehydrogenase in the TCA cycle.
Correct answer is: Succinate dehydrogenase
Q.16 Which molecule is an allosteric activator of PFK-1?
Citrate
ATP
AMP
NADH
Explanation - PFK-1 is activated by high AMP, indicating low energy status, and inhibited by ATP and citrate.
Correct answer is: AMP
Q.17 Fatty acid β-oxidation occurs in the:
Cytosol
Mitochondrial matrix
Endoplasmic reticulum
Nucleus
Explanation - Fatty acid β-oxidation takes place in the mitochondrial matrix, producing acetyl-CoA, NADH, and FADH2.
Correct answer is: Mitochondrial matrix
Q.18 Which of the following cannot be converted into glucose via gluconeogenesis?
Lactate
Glycerol
Alanine
Fatty acids
Explanation - Fatty acids generally cannot serve as substrates for gluconeogenesis, except odd-chain fatty acids which yield propionyl-CoA.
Correct answer is: Fatty acids
Q.19 What is the major product of the oxidative phase of the pentose phosphate pathway?
NADPH
NADH
ATP
FADH2
Explanation - The oxidative phase produces NADPH, which is essential for fatty acid synthesis and maintaining reduced glutathione.
Correct answer is: NADPH
Q.20 In which organelle does the urea cycle take place?
Cytosol
Mitochondria and cytosol
Golgi apparatus
Endoplasmic reticulum
Explanation - The urea cycle spans both the mitochondrial matrix (initial steps) and cytosol (later steps).
Correct answer is: Mitochondria and cytosol
Q.21 Which amino acid is the main carrier of nitrogen in blood?
Alanine
Glutamine
Aspartate
Glycine
Explanation - Glutamine carries excess ammonia from peripheral tissues to the liver for detoxification in the urea cycle.
Correct answer is: Glutamine
Q.22 Which coenzyme is essential for transamination reactions?
Pyridoxal phosphate
Thiamine pyrophosphate
FAD
NAD+
Explanation - Pyridoxal phosphate (active form of vitamin B6) is the coenzyme for aminotransferases in amino acid metabolism.
Correct answer is: Pyridoxal phosphate
Q.23 Which metabolic pathway is activated during fasting?
Glycolysis
Glycogen synthesis
Gluconeogenesis
Fatty acid synthesis
Explanation - During fasting, gluconeogenesis is upregulated to maintain blood glucose levels.
Correct answer is: Gluconeogenesis
Q.24 Which enzyme catalyzes the first step of the urea cycle?
Arginase
Carbamoyl phosphate synthetase I
Ornithine transcarbamylase
Argininosuccinate lyase
Explanation - Carbamoyl phosphate synthetase I catalyzes the condensation of ammonia and CO2 to form carbamoyl phosphate, the first step of the urea cycle.
Correct answer is: Carbamoyl phosphate synthetase I
Q.25 Which of the following is an essential amino acid?
Alanine
Glycine
Lysine
Tyrosine
Explanation - Lysine is an essential amino acid that cannot be synthesized by humans and must be obtained from the diet.
Correct answer is: Lysine