Krebs Cycle -- The Heart of Intermediary Metabolism

Vijay Aswani, PhD


March 10, 2010

Krebs Cycle -- The Heart of Intermediary Metabolism

The Krebs cycle represents a common meeting place of carbohydrate, lipid, and protein metabolism. It variously serves as a means to produce energy, generate intermediates, and convert molecules from one class to another. How well do you know this important pathway?

An unavailability of lipoic acid would hamper the function of which one of the following citric acid cycle enzymes?

  1. Succinate dehydrogenase

  2. Isocitrate dehydrogenase

  3. Alpha-ketoglutarate dehydrogenase

  4. Pyruvate dehydrogenase

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The single substrate-level phosphorylation step of the TCA cycle is catalyzed by:

  1. Alpha-ketoglutarate dehydrogenase

  2. Fumarase

  3. Citrate synthase

  4. Pyruvate kinase

  5. Succinyl CoA thiokinase

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The step in the TCA cycle that involves oxidative decarboxylation of a TCA intermediate that would be hampered by unavailability of a coenzyme is:

  1. Isocitrate dehydrogenase

  2. Alpha-ketoglutarate dehydrogenase

  3. Succinate dehydrogenase

  4. Both A and B

  5. Both B and C

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The total yield of ATP from the Krebs cycle per molecule of acetyl CoA is:

  1. 6-8

  2. 12

  3. 36-38

  4. 14

  5. 24

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All of the following would act as inhibitors of the enzyme citrate synthase in the Krebs cycle EXCEPT:

  1. ATP

  2. NADH

  3. Succinyl CoA

  4. ADP

  5. All of the above are inhibitors

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