Question 1

Which enzyme catalyzes the conversion of malate to oxaloacetate in the citric acid cycle, and what is the main product of this reaction?

Accepted Answer

Malate dehydrogenase; NADH

Question 2

During the conversion of fumarate to L-malate, what is the role of water in the reaction?

Accepted Answer

Water is added in two parts: first as OH-, then as H+

Question 3

How many ATP molecules are ultimately generated from one NADH produced in the citric acid cycle?

Accepted Answer

$$2.5$$

Question 4

Which of the following best describes the fate of the carbons from acetyl-CoA in the citric acid cycle?

Accepted Answer

They are released as CO2 during the cycle

Question 5

If a mutation causes malate dehydrogenase to lose function, which of the following would most likely occur?

Accepted Answer

Accumulation of malate and decreased NADH production

Question 6

Which reaction in the citric acid cycle is directly responsible for the regeneration of oxaloacetate?

Accepted Answer

Malate $$+\ NAD^+\ \rightarrow$$ oxaloacetate $$+\ NADH\ +\ H^+$$

Question 7

Which of the following statements about the regulation of the citric acid cycle is correct?

Accepted Answer

The cycle is inhibited by high levels of ATP and NADH

Question 8

A patient has a deficiency in the enzyme fumarase. Which step of the citric acid cycle is directly affected?

Accepted Answer

Conversion of fumarate to malate

Question 9

Which of the following best explains why the citric acid cycle is considered amphibolic?

Accepted Answer

It functions in both catabolic and anabolic pathways

Question 10

How many ATP equivalents are produced from the complete oxidation of one glucose molecule through glycolysis, pyruvate dehydrogenase, and the citric acid cycle?

Accepted Answer

$$30 to$$ $$32$$ ATP

Question 11

Which of the following is NOT a direct function of the citric acid cycle?

Accepted Answer

Direct synthesis of glucose from pyruvate

Question 12

Which molecule acts as a key activator of the citric acid cycle by stimulating isocitrate dehydrogenase?

Accepted Answer

ADP

Question 13

Which of the following best describes the role of the citric acid cycle in fatty acid metabolism?

Accepted Answer

It provides intermediates for fatty acid biosynthesis

Question 14

If the electron transport chain is inhibited, what is the most immediate effect on the citric acid cycle?

Accepted Answer

Accumulation of NADH and inhibition of the cycle

Question 15

Which of the following reactions in the citric acid cycle is most strongly inhibited by high concentrations of NADH?

Accepted Answer

Isocitrate $$\rightarrow$$ alpha-ketoglutarate

Citric Acid Cycle: Key Reactions and Energetics

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