Q: What is the ΔG°' value for the reaction catalyzed by citrate synthase, and what does this indicate about the reaction's spontaneity under standard conditions?

$\Delta G^\circ' = -32.3\ \text{kJ/mol}$; the reaction is spontaneous

Question 1

Which enzyme catalyzes the first step of the citric acid cycle, and what are the substrates and products of this reaction?

Accepted Answer

Citrate synthase; acetyl-CoA and oxaloacetate to citrate

Question 2

What is the ΔG°' value for the reaction catalyzed by citrate synthase, and what does this indicate about the reaction's spontaneity under standard conditions?

Accepted Answer

$\Delta G^\circ' = -32.3\ 	ext{kJ/mol}$; the reaction is spontaneous

Question 3

During the conversion of citrate to isocitrate, which intermediate is formed and what is the role of water in this process?

Accepted Answer

Cis-aconitate; water is removed and then added

Question 4

Which of the following statements about the reaction catalyzed by aconitase is correct?

Accepted Answer

It involves the isomerization of citrate to isocitrate via cis-aconitate

Question 5

In the citric acid cycle, which step is the first to generate NADH, and what is the enzyme responsible?

Accepted Answer

Isocitrate dehydrogenase; third step

Question 6

What is the role of NAD$^+$ in the reaction catalyzed by isocitrate dehydrogenase?

Accepted Answer

It acts as an electron acceptor, being reduced to NADH

Question 7

Which of the following best describes the fate of CoA in the citrate synthase reaction?

Accepted Answer

CoA is released as a product

Question 8

Why is citrate considered a prochiral molecule, and what is the significance of this in metabolism?

Accepted Answer

It has two identical carboxymethyl groups, allowing for stereospecific enzyme reactions

Question 9

Which of the following is NOT a product of the isocitrate dehydrogenase reaction?

Accepted Answer

FADH$_2$

Question 10

A patient has a mutation that reduces the activity of aconitase. Which of the following would most likely accumulate in their mitochondria?

Accepted Answer

Citrate

Question 11

Which step in the citric acid cycle involves both oxidation and decarboxylation?

Accepted Answer

Isocitrate dehydrogenase

Question 12

If the supply of NAD$^+$ is limited in the mitochondria, which reaction in the citric acid cycle would be directly affected?

Accepted Answer

Isocitrate dehydrogenase

Question 13

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

Accepted Answer

Citrate is too stable to be directly oxidized

Question 14

Which of the following correctly matches the enzyme with its function in the citric acid cycle?

Accepted Answer

Isocitrate dehydrogenase: catalyzes the oxidative decarboxylation of isocitrate

Question 15

Which molecule is produced in the citric acid cycle and is a key intermediate for amino acid biosynthesis?

Accepted Answer

$\alpha$-ketoglutarate

Citric Acid Cycle: Key Steps and Mechanisms

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