In the presence of oxygen, the three-carbon compound pyruvate can be catabolized in the citric acid cycle. First, however, the pyruvate (1) loses a carbon, (2) is oxidized to form a two-carbon compound, which (3) is covalently bound to coenzyme A. These three steps result in the formation of
A) acetyl CoA, CO₂, and ATP.
B) acetyl CoA, FADH₂, and CO₂.
C) acetyl CoA, NADH, H2, and CO₂.
D) acetyl CoA, NADH, H+, and CO₂.
E) acetyl CoA, NAD+, ATP, and CO₂.

Question

Quizplus · Accepted Answer

The three steps of pyruvate catabolism described in the question result in the formation of acetyl CoA, NADH, H+, and CO₂. This is because the loss of a carbon from pyruvate results in the release of CO₂, the oxidation of the two-carbon compound to acetyl CoA results in the reduction of NAD+ to NADH and the release of an H+, and the covalent bonding of the acetyl group to CoA results in the formation of acetyl CoA. Therefore, choice D is the best answer. Choice A is incorrect because ATP is not formed during pyruvate catabolism. Choice B is incorrect because FADH₂ is not formed during the catabolism of pyruvate. Choice C is incorrect because H2 (hydrogen gas) is not formed during pyruvate catabolism. Choice E is incorrect because ATP is not formed during pyruvate catabolism.

In the Presence of Oxygen, the Three-Carbon Compound Pyruvate Can