Q: Which of the following is a correct balanced equation for the overall products generated from one acetyl-CoA entering the citric acid cycle?

$\text{Acetyl-CoA} + 3\text{NAD}^+ + \text{FAD} + \text{GDP} + \text{P}_i + 2\text{H}_2\text{O} \rightarrow 2\text{CO}_2 + 3\text{NADH} + 3\text{H}^+ + \text{FADH}_2 + \text{GTP} + \text{CoA-SH}$

Question 1

Which of the following statements best explains why the reactions at steps 1, 3, and 4 of the citric acid cycle are considered to drive the cycle forward?

Accepted Answer

They have a highly negative $\Delta G$, making them essentially irreversible under cellular conditions.

Question 2

During one turn of the citric acid cycle, how many NADH molecules are produced?

Accepted Answer

3

Question 3

Which intermediate of the citric acid cycle is directly involved in the substrate-level phosphorylation that generates GTP?

Accepted Answer

Succinyl-CoA

Question 4

If a mutation prevents the conversion of succinate to fumarate, which molecule's production would be directly affected?

Accepted Answer

FADH$_2$

Question 5

Which step in the citric acid cycle involves the release of CO$_2$ and the reduction of NAD$^+$ to NADH?

Accepted Answer

Conversion of isocitrate to $	ext{α}$-ketoglutarate

Question 6

Which of the following best describes the fate of the labeled carbons from acetyl-CoA after one turn of the citric acid cycle?

Accepted Answer

Neither labeled carbon is released as CO$_2$ in the first turn due to the randomization of succinate's orientation.

Question 7

Which enzyme catalyzes the conversion of malate to oxaloacetate, and what is the associated redox reaction?

Accepted Answer

Malate dehydrogenase; reduction of NAD$^+$ to NADH

Question 8

Which of the following is a correct balanced equation for the overall products generated from one acetyl-CoA entering the citric acid cycle?

Accepted Answer

$	ext{Acetyl-CoA} + 3	ext{NAD}^+ + 	ext{FAD} + 	ext{GDP} + 	ext{P}_i + 2	ext{H}_2	ext{O} ightarrow 2	ext{CO}_2 + 3	ext{NADH} + 3	ext{H}^+ + 	ext{FADH}_2 + 	ext{GTP} + 	ext{CoA-SH}$

Question 9

A patient presents with a deficiency in the enzyme isocitrate dehydrogenase. Which of the following would most likely accumulate in their cells?

Accepted Answer

Isocitrate

Question 10

Which of the following steps in the citric acid cycle is most likely to be regulated by feedback inhibition from high levels of ATP?

Accepted Answer

Conversion of oxaloacetate and acetyl-CoA to citrate

Question 11

Which molecule is regenerated at the end of the citric acid cycle, allowing the cycle to continue?

Accepted Answer

Oxaloacetate

Question 12

In the citric acid cycle, which step is directly responsible for the production of FADH$_2$?

Accepted Answer

Conversion of succinate to fumarate

Question 13

Which of the following is NOT a product of the citric acid cycle per acetyl-CoA molecule?

Accepted Answer

Pyruvate

Question 14

A researcher labels the carbons of acetyl-CoA and tracks their fate through the citric acid cycle. After one turn, what is the most accurate statement about the fate of these carbons?

Accepted Answer

Neither is released as CO$_2$ in the first turn.

Question 15

Which of the following best explains why steps 2, 6, 7, and 8 of the citric acid cycle are readily reversible?

Accepted Answer

They have a $\Delta G$ close to zero.

Question 16

Which of the following is a direct consequence of the randomization of succinate's orientation in the citric acid cycle?

Accepted Answer

It prevents the immediate release of both acetyl-CoA carbons as CO$_2$.

Question 17

Which of the following is the correct order of intermediates in the citric acid cycle starting from citrate?

Accepted Answer

Citrate → Isocitrate → $	ext{α}$-Ketoglutarate → Succinyl-CoA → Succinate → Fumarate → Malate → Oxaloacetate

Citric Acid Cycle: Structure, Energetics, and Carbon Fate

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