All Free Biochemistry MCQs with Answers

• A. Muscle
• B. All of the above
• C. Heart
• D. RBC

Explanation: Mature red blood cells lack mitochondria, so they cannot carry out the mitochondrial TCA cycle and depend on glycolysis for ATP.

• A. Citrate
• B. Isocitrate
• C. Succinate
• D. Fumarate

Explanation: Citrate is the first compound formed when acetyl-CoA condenses with oxaloacetate in the TCA cycle.

• A. Alpha ketoglutrate to succinyl CoA
• B. Succinyl CoA to Succinate
• C. Succinate to fumarate
• D. Oxalocetate to citrate

Explanation: Substrate-level phosphorylation in the TCA cycle occurs when succinyl-CoA is converted to succinate, producing GTP or ATP directly.

• A. Nucleus
• B. Ribosomes
• C. Mitochondria
• D. Nonparticulate cytoplasm

Explanation: In eukaryotic cells, most citric acid cycle enzymes are located in the mitochondrial matrix, while succinate dehydrogenase is embedded in…

• A. Oleic acid
• B. Alanine
• C. Glycerol
• D. Tryptophan

Explanation: Oleic acid is an even-chain fatty acid whose acetyl-CoA products cannot give a net synthesis of glucose in humans.

• A. 2- phospho glyceric acid
• B. Dihydroxy acetone phosphate
• C. 3- phospho glyceralehyde
• D. 3- phospho glyceric acid

Explanation: Glycerol is converted to glycerol 3-phosphate and then oxidised to dihydroxyacetone phosphate, which is a glycolytic intermediate.

• A. Amino acids
• B. Glycerol
• C. Acetoacetate
• D. Lactic acid

Explanation: Amino acids, glycerol and lactate can enter gluconeogenic pathways and form glucose.

• A. Alanine
• B. Glycerol
• C. Ketones
• D. Lactate

Explanation: Lactate makes a major contribution to gluconeogenesis through the Cori cycle: the liver converts lactate from exercising muscle and red…

• A. Glucose
• B. Ketone bodies
• C. Fructose
• D. Fatty acids

Explanation: During prolonged starvation, the brain adapts to use ketone bodies made by the liver, greatly reducing its dependence on glucose.

• A. Enzymes
• B. Vitamins
• C. Minerals
• D. None of the above

Explanation: The citric acid cycle is the final common oxidative pathway for carbohydrates, fatty acids and many amino acids, but none of these…

• A. Lactate dehydrogenase
• B. Pyruvate kinase
• C. Pyruvate dehydrogenase
• D. Citrate synthase

Explanation: The pyruvate dehydrogenase complex converts glycolytic pyruvate into acetyl-CoA, which enters the citric acid cycle.

• A. Vitamin C
• B. Pyridoxine
• C. Niacin
• D. Thiamine

Explanation: Thiamine pyrophosphate is required by pyruvate dehydrogenase, so thiamine deficiency blocks conversion of pyruvate to acetyl-CoA.

• A. Krebs cylce
• B. EMP pathway
• C. Urea cycle
• D. Electron transfer

Explanation: The Embden-Meyerhof pathway, or glycolysis, occurs in the cytosol. The Krebs cycle and electron-transfer chain occur in mitochondria…

• A. NADPH
• B. D fructose 6 phosphate
• C. D sedoheptulose 5 phosphate
• D. D glyceraldehyde 3 phosphate

Explanation: The HMP shunt produces NADPH and intermediates such as fructose-6-phosphate, glyceraldehyde-3-phosphate, and sedoheptulose-7-phosphate.

• A. Enolase
• B. Phosphoglycero mutase
• C. Aldolase
• D. Glycerophosphate dehydrogenase

Explanation: Enolase, phosphoglycerate mutase and aldolase are glycolytic enzymes. Glycerophosphate dehydrogenase functions mainly in the…

• A. Glycolysis
• B. Gluconeogenesis
• C. Beta oxidation
• D. TCA cycle

Explanation: Phosphofructokinase-1 catalyses the major rate-limiting and committed step of glycolysis, converting fructose-6-phosphate to…

• A. Oxalocetate
• B. Ornithine
• C. Alpha ketoglutarate
• D. Glycine

Explanation: Alpha-ketoglutarate accepts amino groups to form glutamate, and glutamate then binds ammonia to form glutamine for safe transport in the…

• A. Isocitrate
• B. Glutarate
• C. Oxalocetate
• D. Cisaconitate

Explanation: Aconitase first removes water from citrate to form cis-aconitate, then adds water to produce isocitrate.

• A. Thiokinase
• B. Malonate reduction
• C. Succinate dehydrogenase
• D. None of the above

Explanation: Substrate-level phosphorylation in the TCA cycle occurs when succinyl-CoA is converted to succinate by succinyl-CoA synthetase, also…

• A. Pyruvic acid
• B. Lactic acid
• C. Acetoacetic acid
• D. Oxaloacetic acid

Explanation: When oxygen is insufficient, pyruvate is reduced to lactate so NAD+ is regenerated and glycolysis can continue.