Question 1

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

Accepted Answer

It converts pyruvate into acetyl-CoA, linking glycolysis to the citric acid cycle.

Question 2

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

Accepted Answer

FADH$$_2$$

Question 3

Which cofactor is NOT required by the pyruvate dehydrogenase complex?

Accepted Answer

Biotin

Question 4

The conversion of pyruvate to acetyl-CoA is regulated by which of the following molecules?

Accepted Answer

ATP and NADH (negative regulation)

Question 5

Which of the following statements about the fate of carbons from glucose in acetyl-CoA is correct?

Accepted Answer

Acetyl-CoA contains carbons 1 and 2 from glucose, while carbon 3 is released as CO$$_2.$$

Question 6

Which enzyme component of the pyruvate dehydrogenase complex is responsible for the decarboxylation of pyruvate?

Accepted Answer

E1: Pyruvate dehydrogenase

Question 7

A patient with a deficiency in thiamine (vitamin B1) would most likely have impaired activity of which enzyme complex?

Accepted Answer

Pyruvate dehydrogenase complex

Question 8

Which of the following best explains why the pyruvate dehydrogenase reaction is considered irreversible under physiological conditions?

Accepted Answer

The large negative free energy change ($$ \Delta G^\circ' = -33.4  kJ/$$mol) makes the reaction highly exergonic.

Question 9

Which of the following is a correct sequence of events in the pyruvate dehydrogenase complex?

Accepted Answer

Decarboxylation of pyruvate, transfer of acetyl group to CoA, reduction of NAD$$ ^+ $$

Question 10

If the activity of the pyruvate dehydrogenase complex is inhibited, which of the following is most likely to accumulate in the cell?

Accepted Answer

Pyruvate

Question 11

Which of the following best describes the location of the pyruvate dehydrogenase complex in eukaryotic cells?

Accepted Answer

Mitochondrial matrix

Question 12

Which of the following molecules is a positive regulator of the pyruvate dehydrogenase complex?

Accepted Answer

ADP

Question 13

A mutation that decreases the affinity of E2 (dihydrolipoyl transacetylase) for lipoic acid would most directly affect which step of the pyruvate dehydrogenase reaction?

Accepted Answer

Transfer of the acetyl group to CoA

Question 14

Which of the following best explains why fatty acids inhibit the pyruvate dehydrogenase complex?

Accepted Answer

Fatty acids signal that there is sufficient energy, reducing the need for acetyl-CoA production from carbohydrates.

Question 15

Which of the following is the correct balanced equation for the pyruvate dehydrogenase reaction?

Accepted Answer

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

Pyruvate Oxidation and Acetyl-CoA Formation

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