Q: What is the net reaction catalyzed by the pyruvate dehydrogenase complex?

$$\text{Pyruvate} + \text{NAD}^+ + \text{CoA-SH} \rightarrow \text{Acetyl-CoA} + \text{CO}_2 + \text{NADH} + \text{H}^+$$

Question 1

Which of the following best describes the primary function of the pyruvate dehydrogenase complex in cellular metabolism?

Accepted Answer

It catalyzes the oxidative decarboxylation of pyruvate to acetyl-CoA and CO$$_2$$, linking glycolysis to the citric acid cycle.

Question 2

Which coenzyme is directly involved in the decarboxylation of pyruvate by the pyruvate dehydrogenase complex?

Accepted Answer

Thiamine pyrophosphate (TPP)

Question 3

What is the net reaction catalyzed by the pyruvate dehydrogenase complex?

Accepted Answer

$$	ext{Pyruvate} + 	ext{NAD}^+ + 	ext{CoA-SH} ightarrow 	ext{Acetyl-CoA} + 	ext{CO}_2 + 	ext{NADH} + 	ext{H}^+$$

Question 4

Which of the following statements about the regulation of the pyruvate dehydrogenase complex is CORRECT?

Accepted Answer

It is allosterically inhibited by NADH and acetyl-CoA.

Question 5

Which of the following is a direct product of the citric acid cycle that is used in the electron transport chain?

Accepted Answer

NADH

Question 6

A patient has a deficiency in lipoamide, a cofactor in the pyruvate dehydrogenase complex. Which step would be directly affected?

Accepted Answer

Transfer of the acetyl group from hydroxyethyl-TPP to lipoamide

Question 7

Which enzyme catalyzes the transfer of electrons from FADH$$_2 to $$NAD$$^+ in $$the pyruvate dehydrogenase complex?

Accepted Answer

E3 (Dihydrolipoyl dehydrogenase)

Question 8

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

Accepted Answer

It serves both catabolic and anabolic roles in metabolism.

Question 9

If the mitochondrial matrix concentration of NADH becomes very high, what is the most likely effect on the pyruvate dehydrogenase complex?

Accepted Answer

It will be inhibited, slowing the conversion of pyruvate to acetyl-CoA.

Question 10

Which of the following is NOT a direct fate of acetyl-CoA produced by the pyruvate dehydrogenase complex?

Accepted Answer

Conversion to glucose via gluconeogenesis

Question 11

Which of the following best describes the role of thiamine pyrophosphate (TPP) in the pyruvate dehydrogenase complex?

Accepted Answer

It stabilizes the carbanion intermediate during decarboxylation of pyruvate.

Question 12

Which of the following is the correct sequence of electron flow in the pyruvate dehydrogenase complex?

Accepted Answer

Lipoamide $$\rightarrow$$ FAD $$\rightarrow$$ NAD^+$

Question 13

Which of the following would most likely result from a genetic mutation that inactivates pyruvate dehydrogenase kinase?

Accepted Answer

Increased activity of the pyruvate dehydrogenase complex due to decreased phosphorylation

Question 14

Which of the following best explains why the conversion of pyruvate to acetyl-CoA is considered irreversible under physiological conditions?

Accepted Answer

The reaction is highly exergonic and CO$$_2 is $$released, which cannot be recaptured by the cell.

Question 15

Which of the following is a key regulatory effect of high ATP concentrations on the pyruvate dehydrogenase complex?

Accepted Answer

Inhibition of the complex by stimulating pyruvate dehydrogenase kinase

Question 16

A patient with a deficiency in the E3 subunit of the pyruvate dehydrogenase complex would most likely exhibit which of the following symptoms?

Accepted Answer

Accumulation of pyruvate and lactic acidosis

Question 17

Which of the following best describes the role of lipoamide in the pyruvate dehydrogenase complex?

Accepted Answer

It acts as a swinging arm to transfer the acetyl group between active sites.

Question 18

Which of the following is the correct net equation for the citric acid cycle per acetyl-CoA molecule?

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 19

Which of the following statements about the transport of pyruvate into mitochondria is CORRECT?

Accepted Answer

Pyruvate is transported into the mitochondrial matrix by a specific carrier protein.

The Aerobic Fate of Pyruvate and the Citric Acid Cycle

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