All Free Biochemistry MCQs with Answers

• A. ATP
• B. TTP
• C. ITP
• D. GTP

Explanation: Succinyl-CoA synthetase produces GTP from GDP and inorganic phosphate by substrate-level phosphorylation in the citric acid cycle.

• A. Oxaloacetic acid
• B. Glutamic acid
• C. Nitric acid
• D. None of the above

Explanation: Oxaloacetic acid is regenerated at the end of the citric acid cycle when malate is oxidized.

• A. Anaerobic
• B. Aerobic
• C. Microaerophilic
• D. Aerobic and anaerobic

Explanation: The citric acid cycle is considered aerobic because it depends on oxygen indirectly through the electron transport chain, which reoxidizes…

• A. Glucose 6 phosphatase
• B. Hexokinase
• C. Glucokinase
• D. Adenylate kinase

Explanation: Insulin increases hepatic glucokinase expression and activity, promoting glucose phosphorylation and glycolysis after a meal.

• A. Glucokinase
• B. Hexokinase
• C. Glucose diphosphatase
• D. Phosphorylase

Explanation: Adrenaline stimulates glycogen phosphorylase through the cAMP-dependent phosphorylation cascade, causing glycogen breakdown.

• A. Fat
• B. Muscle
• C. Heart
• D. Kidney

Explanation: Gluconeogenesis occurs mainly in the liver and, especially during fasting, in the kidney cortex.

• A. Muscle lacks glucose 6 phosphatase
• B. Muscle lacks phospho gluco isomerase
• C. Absence of glucokinase
• D. Muscle does not contain glycogen phosphorylase

Explanation: Muscle can break glycogen down to glucose 6-phosphate, but it lacks glucose 6-phosphatase.

• A. ATPase
• B. Enolase
• C. Pyruvate Kinase
• D. Fructose 6 phosphatase

Explanation: Fluoride inhibits enolase, the glycolytic enzyme that converts 2-phosphoglycerate to phosphoenolpyruvate.

• A. It is present in cytoplasm
• B. Catalyzes the conversion of pyruvate to oxaloacetate
• C. Requires TPP as cofactor
• D. Catalyzes a reversible reaction

Explanation: Pyruvate dehydrogenase is a mitochondrial complex that irreversibly converts pyruvate to acetyl-CoA, not oxaloacetate.

• A. Mitochondria
• B. Nucleus
• C. Ribosomes
• D. Non-particulate cytoplasm

Explanation: Most citric acid cycle enzymes are located in the mitochondrial matrix, while succinate dehydrogenase is embedded in the inner…

• A. HMG-Co A synthase
• B. Malic enzyme
• C. Malonyl CoA synthetase
• D. Fatty acid synthetase

Explanation: Malic enzyme uses malate and NADP+ to form pyruvate, so acetyl-CoA is not its substrate.

• A. Dopamine hydroxylase
• B. Dopa decarboxylase
• C. O-methylation
• D. N-methylation

Explanation: Norepinephrine becomes epinephrine when a methyl group is added to its amino group by phenylethanolamine N-methyltransferase.

• A. Tyrosine to dopa
• B. Phenylalanine to tyrosine
• C. Dopa to dopamine
• D. Dopamine to nor epinephrine

Explanation: Tyrosine hydroxylase converts tyrosine to DOPA and catalyses the rate-limiting step of catecholamine synthesis.

• A. Insulin
• B. GH
• C. Glucagon
• D. Androgen

Explanation: Glucagon promotes fatty-acid breakdown and hepatic ketone-body formation during fasting, so it has a ketogenic effect.

• A. Metabolic acidosis
• B. Smell of acetone in breath
• C. Rothera's test is +ve
• D. Benedict's test +ve

Explanation: Starvation ketoacidosis causes metabolic acidosis, acetone-smelling breath, and a positive Rothera test for ketone bodies.

• A. Ubiquinone
• B. Cytochrome Cl
• C. Flavoprotein
• D. Cytochrome A

Explanation: Ubiquinone, or coenzyme Q, is a relatively mobile, lipid-soluble electron carrier within the inner mitochondrial membrane.

• A. 1 mg%
• B. 5 mg%
• C. 12 mg%
• D. 20 mg%

Explanation: In a well-fed person, ketone-body production is minimal and the total blood concentration is about 1 mg%, unlike fasting or diabetic…

• A. Pyridoxin
• B. Niacin
• C. Retinotic acid
• D. Thiamine

Explanation: Thiamine pyrophosphate is required by pyruvate dehydrogenase, so its deficiency blocks pyruvate oxidation and causes accumulation of…

• A. All of the above
• B. Lipid
• C. Amino acids
• D. Carbohydrate

Explanation: Acetyl-CoA is a central fuel-derived molecule formed from pyruvate from carbohydrates, beta-oxidation of lipids, and ketogenic amino…

• A. Brain
• B. Liver
• C. Kidney
• D. Spleen

Explanation: The liver produces ketone bodies but cannot use them because it lacks thiophorase, the enzyme needed to convert acetoacetate into an…