Question 1

Which enzyme catalyzes the highly exergonic entry step of the TCA cycle, and what is the approximate standard free energy change ($$\Delta G$$^{\circ'}$$) for this reaction?

Accepted Answer

Citrate synthase; $$\Delta G$$^{\circ'}$$ = -31.5 kJ/$$mol

Question 2

What is the primary fate of pyruvate after it enters the mitochondria via the mitochondrial pyruvate carrier (MPC) under aerobic conditions?

Accepted Answer

Conversion to acetyl-CoA by pyruvate dehydrogenase (PDH)

Question 3

Which of the following best describes the role of succinate dehydrogenase in cellular metabolism?

Accepted Answer

It catalyzes a reaction in the TCA cycle and is also part of the electron transport chain.

Question 4

Which TCA cycle enzyme is most directly responsible for the generation of GTP, and what is the reaction it catalyzes?

Accepted Answer

Succinyl-CoA synthetase; succinyl-CoA to succinate

Question 5

Why is the malate dehydrogenase reaction in the TCA cycle able to proceed despite its large positive standard free energy change ($$\Delta G$$^{\circ'}$$)?

Accepted Answer

Because oxaloacetate is rapidly consumed by citrate synthase, pulling the reaction forward.

Question 6

Which of the following statements about the mitochondrial pyruvate carrier (MPC) is correct?

Accepted Answer

It transports pyruvate from the cytosol into the mitochondrial matrix.

Question 7

A patient with a deficiency in pyruvate dehydrogenase (PDH) would most likely exhibit which of the following metabolic consequences?

Accepted Answer

Increased conversion of pyruvate to lactate

Question 8

Which TCA cycle intermediate can be exported to the cytosol for fatty acid biosynthesis, and by which shuttle mechanism?

Accepted Answer

Citrate; citrate shuttle

Question 9

Which of the following best explains why the TCA cycle is considered a metabolic hub?

Accepted Answer

It connects carbohydrate, fat, and amino acid metabolism, providing intermediates for biosynthesis and energy production.

Question 10

Which enzyme complex is responsible for the oxidative decarboxylation of pyruvate, and what are its three main enzymatic components?

Accepted Answer

Pyruvate dehydrogenase complex; E1 (pyruvate dehydrogenase), E2 (dihydrolipoyl transacetylase), E3 (dihydrolipoyl dehydrogenase)

Question 11

Which of the following is a direct consequence of increased reactive oxygen species (ROS) production in mitochondria?

Accepted Answer

Activation of apoptotic signaling pathways

Question 12

In the context of metabolic reprogramming in cancer cells, which alternative carbon source is often used to replenish TCA cycle intermediates?

Accepted Answer

Glutamine

Question 13

Which TCA cycle reaction is most similar in mechanism to the pyruvate dehydrogenase complex?

Accepted Answer

Alpha-ketoglutarate dehydrogenase

Question 14

A mutation that impairs the function of the malate-aspartate shuttle would most directly affect which process?

Accepted Answer

Transfer of cytosolic NADH electrons into the mitochondria

Question 15

Which of the following best describes the energetic strategy of the TCA cycle?

Accepted Answer

It couples decarboxylation reactions to the reduction of NAD+ and FAD, generating NADH and FADH2 for the electron transport chain.

Question 16

Which TCA cycle enzyme catalyzes a reaction with a positive standard free energy change ($$\Delta G$$^{\circ'}$$), and what is the physiological significance?

Accepted Answer

Malate dehydrogenase; the reaction is pulled forward by rapid consumption of oxaloacetate

Question 17

Which of the following best explains why the TCA cycle is central to both energy production and biosynthesis?

Accepted Answer

It provides intermediates for amino acid, nucleotide, and fatty acid biosynthesis.

Question 18

Which of the following is a key regulatory mechanism of the TCA cycle in response to cellular energy needs?

Accepted Answer

Allosteric inhibition of isocitrate dehydrogenase by ATP

Question 19

A patient with a mitochondrial disorder affecting the electron transport chain (ETC) would most likely experience which of the following?

Accepted Answer

Decreased ATP production and increased ROS generation

TCA Cycle: Chemical Strategy, Regulation, and Mitochondrial Connections

Study Guide - Practice Questions

Study Guide - Flashcards