Question 1

Which of the following best describes the fate of pyruvate under anaerobic conditions in mammalian muscle cells?

Accepted Answer

Pyruvate is converted to lactate.

Question 2

Which enzyme catalyzes the only reaction in the citric acid cycle that forms a carbon-carbon bond?

Accepted Answer

Citrate synthase

Question 3

What is the primary function of the citric acid cycle in cellular metabolism?

Accepted Answer

To oxidize acetyl CoA to CO$$_2$$ and generate reduced coenzymes for ATP production

Question 4

Which of the following statements about the citric acid cycle is TRUE?

Accepted Answer

It is amphibolic, serving both catabolic and anabolic roles.

Question 5

How many NADH molecules are produced per acetyl CoA that enters the citric acid cycle?

Accepted Answer

3

Question 6

Which reaction in the citric acid cycle is directly coupled to the substrate-level phosphorylation of GDP to GTP?

Accepted Answer

Succinyl-CoA to succinate

Question 7

A patient has a genetic defect in the pyruvate dehydrogenase complex. Which of the following would most likely accumulate in their cells?

Accepted Answer

Pyruvate

Question 8

Which coenzyme is reduced during the conversion of isocitrate to α-ketoglutarate in the citric acid cycle?

Accepted Answer

NAD+

Question 9

Which of the following best explains why the citric acid cycle is considered a 'hub' of metabolism?

Accepted Answer

It integrates the catabolism of carbohydrates, lipids, and amino acids, and provides intermediates for biosynthesis.

Question 10

Which of the following reactions in the citric acid cycle involves the reduction of ubiquinone (Q) to QH$$_2$$?

Accepted Answer

Succinate to fumarate

Question 11

A mutation in the gene encoding fumarase would most directly affect which step of the citric acid cycle?

Accepted Answer

Conversion of fumarate to L-malate

Question 12

Which of the following best describes the role of the thioester bond in succinyl-CoA during the citric acid cycle?

Accepted Answer

It is hydrolyzed to drive the phosphorylation of GDP to GTP.

Question 13

Which of the following is NOT a product of one turn of the citric acid cycle per acetyl CoA?

Accepted Answer

2 GTP

Question 14

Which step in the citric acid cycle is considered metabolically irreversible and why?

Accepted Answer

Citrate synthase reaction, due to the hydrolysis of a thioester bond

Question 15

Which of the following best explains why the conversion of citrate to isocitrate is necessary in the citric acid cycle?

Accepted Answer

To prepare the molecule for decarboxylation and oxidation of a secondary alcohol

Question 16

Which of the following statements about the transport of pyruvate into the mitochondria is correct?

Accepted Answer

Pyruvate is transported through the inner mitochondrial membrane by pyruvate translocase symport with H+.

Question 17

Which of the following is a direct result of the decarboxylation reactions in the citric acid cycle?

Accepted Answer

Release of CO$$_2$$

Question 18

Which of the following best describes the fate of NADH and QH$$_2$$ produced in the citric acid cycle?

Accepted Answer

They are oxidized by the respiratory electron transport chain to generate ATP via oxidative phosphorylation.

The Citric Acid Cycle (TCA/Krebs Cycle): Central Pathway of Aerobic Metabolism

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