citric acid cycle

1. What is the main role of the citric acid cycle?

• A. Production of glucose

• • B. Complete oxidation of acetyl groups to CO₂ and capture of high-energy electrons

• • C. Breakdown of fatty acids into ketones

• • D. Conversion of lactate to pyruvate

2. Which of the following is not an intermediate of the citric acid cycle?

• • A. Citrate

• • B. Oxaloacetate

• • C. Pyruvate

• D. α-Ketoglutarate

3. Which enzyme catalyzes the conversion of isocitrate to α-ketoglutarate?

• A. Citrate synthase

• B. Aconitase

• C. Isocitrate dehydrogenase

• D. Malate dehydrogenase

4. Which of the following is a rate-limiting step of the citric acid cycle?

• • A. Malate → Oxaloacetate

• • B. Succinyl-CoA → Succinate

• • C. Citrate → Isocitrate

• • D. Isocitrate → α-Ketoglutarate

5. What activates isocitrate dehydrogenase?

• • A. ADP

• • B. NADH

• • C. ATP

• • D. Citrate

6. Which of the following molecules is both a substrate and a product in the citric acid cycle?

• • A. Acetyl-CoA

• • B. Oxaloacetate

• • C. NAD⁺

• • D. CO₂

7. The citric acid cycle directly consumes molecular oxygen (O₂).

• True

• False

Answer explanation

The citric acid cycle itself does not consume O₂ directly; oxygen is the final electron acceptor in the electron transport chain.

FADH₂ and NADH produced in the citric acid cycle are used in the electron transport chain.

• True

• False

The enzyme citrate synthase is allosterically inhibited by citrate.

• True

• False

Which of the following shows the correct order of intermediates in the citric acid cycle starting from citrate?

• A. Citrate → Isocitrate →Succinyl-CoA → Isocitrate → Fumarate → Malate → Oxaloacetate

• B. Citrate → Isocitrate → α-Ketoglutarate → Succinyl-CoA → Succinate → Fumarate → Malate → Oxaloacetate

• C. Citrate → Isocitrate → α-Ketoglutarate → Succinate → Malate → Oxaloacetate → Isocitrate

• D. Citrate → Isocitrate → Malate → Succinate → Succinyl-CoA → Isocitrate → α-Ketoglutarate

Answer explanation

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