Q: What is the net equation for the reaction catalyzed by citrate synthase?

$$\text{Acetyl-CoA} + \text{Oxaloacetate} + \text{H}_2\text{O} \rightarrow \text{Citrate} + \text{CoA-SH}$$

Question 1

Which enzyme catalyzes the condensation of acetyl-CoA and oxaloacetate to form citrate in the citric acid cycle?

Accepted Answer

Citrate synthase

Question 2

During which step of the citric acid cycle is GTP produced, and what is the immediate substrate for this reaction?

Accepted Answer

Step 5; Succinyl-CoA

Question 3

Which of the following best describes the reaction catalyzed by aconitase in the citric acid cycle?

Accepted Answer

Isomerization

Question 4

What is the net equation for the reaction catalyzed by citrate synthase?

Accepted Answer

$$	ext{Acetyl-CoA} + 	ext{Oxaloacetate} + 	ext{H}_2	ext{O} ightarrow 	ext{Citrate} + 	ext{CoA-SH}$$

Question 5

Which step in the citric acid cycle is the only one directly associated with substrate-level phosphorylation?

Accepted Answer

Step 5: Succinyl-CoA to Succinate

Question 6

Which enzyme is unique in the citric acid cycle for being an integral protein of the inner mitochondrial membrane and containing covalently bound FAD?

Accepted Answer

Succinate dehydrogenase

Question 7

How many NADH molecules are produced per turn of the citric acid cycle for each acetyl-CoA oxidized?

Accepted Answer

3

Question 8

Which reaction in the citric acid cycle is an example of an oxidative decarboxylation?

Accepted Answer

Isocitrate to α-Ketoglutarate

Question 9

Why is GTP produced by the citric acid cycle considered energetically equivalent to ATP?

Accepted Answer

GTP can be directly converted to ATP by nucleoside diphosphate kinase

Question 10

Which of the following statements about the fate of the two carbons from acetyl-CoA entering the citric acid cycle is correct?

Accepted Answer

They are retained in cycle intermediates during the first turn

Question 11

Which step in the citric acid cycle involves the addition of water across a double bond?

Accepted Answer

Fumarate to Malate

Question 12

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

Accepted Answer

To capture energy as NADH, FADH₂, and GTP for ATP production

Question 13

Which of the following best explains why succinate dehydrogenase uses FAD instead of NAD⁺ as its electron acceptor?

Accepted Answer

The oxidation of succinate does not release enough energy to reduce NAD⁺

Question 14

Which reaction in the citric acid cycle directly regenerates oxaloacetate?

Accepted Answer

L-Malate to Oxaloacetate

Question 15

A patient has a mutation that inactivates the α-ketoglutarate dehydrogenase complex. Which of the following products would be directly decreased in the citric acid cycle?

Accepted Answer

NADH and CO₂

Question 16

Which of the following is NOT a product of a single turn of the citric acid cycle?

Accepted Answer

2 GTP

Question 17

Which enzyme catalyzes a reaction that is both an oxidation and a decarboxylation?

Accepted Answer

Isocitrate dehydrogenase

Question 18

What is the correct sequence of the following intermediates in the citric acid cycle, starting from citrate?

Accepted Answer

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

Question 19

Which of the following best describes the difference between a synthase and a synthetase?

Accepted Answer

A synthase does not require direct input of a high-energy phosphate, while a synthetase does

Question 20

If one molecule of glucose is fully oxidized through glycolysis, pyruvate oxidation, and the citric acid cycle, how many NADH molecules are produced by the citric acid cycle alone?

Accepted Answer

6

Citric Acid Cycle: Individual Reactions and Energy Yield

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