Q: Which of the following best describes the overall reaction of the Citric Acid Cycle?

$$\text{Acetyl-CoA} + 3\ NAD^+ + FAD + GDP + P_i + 2\ H_2O \rightarrow 2\ CO_2$ + 3\ NADH + 3\ H^+ + $$FADH_2$$ + GTP + CoA$$

Question 1

Which of the following is NOT a function of the pyruvate dehydrogenase complex?

Accepted Answer

It generates both NADH and FADH$$_2$$ for the electron transport chain.

Question 2

If glucose labeled at the first and fourth carbons with $$^{14}C is $$converted to pyruvate by glycolysis and then to acetyl-CoA, where will the $$^{14}C $$label appear in the acetyl-CoA molecule?

Accepted Answer

In the methyl group of acetyl-CoA

Question 3

Malonate is a competitive inhibitor of succinate dehydrogenase. If malonate is added to respiring mitochondria, which molecule would you expect to decrease in concentration?

Accepted Answer

Fumarate

Question 4

Which of the following is NOT an intermediate in the Citric Acid Cycle?

Accepted Answer

Acetyl-CoA

Question 5

If oxaloacetate uniformly labeled with $$^{14}C at $$all carbons is added to mitochondria with an adequate supply of acetyl-CoA (unlabeled), after one turn of the cycle, how much radioactivity will remain in oxaloacetate?

Accepted Answer

50\%

Question 6

Which enzyme catalyzes the only substrate-level phosphorylation in the Citric Acid Cycle?

Accepted Answer

Succinate thiokinase (succinyl-CoA synthetase)

Question 7

A patient has a mutation that inactivates the enzyme alpha-ketoglutarate dehydrogenase. Which of the following would you expect to accumulate?

Accepted Answer

Alpha-ketoglutarate

Question 8

Which of the following steps in the Citric Acid Cycle directly produces NADH?

Accepted Answer

$$\alpha-$$ketoglutarate to succinyl-CoA

Question 9

Which molecule is regenerated at the end of the Citric Acid Cycle to combine with acetyl-CoA and begin the cycle again?

Accepted Answer

Oxaloacetate

Question 10

Which of the following best describes the overall reaction of the Citric Acid Cycle?

Accepted Answer

$$	ext{Acetyl-CoA} + 3\ NAD^+ + FAD + GDP + P_i + 2\ H_2O ightarrow 2\ CO_2$ + 3\ NADH + 3\ H^+ + $$FADH_2$$ + GTP + CoA$$

Citric Acid Cycle: Practice Questions and Key Concepts

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