Answer: Pyruvate is further oxidized to acetyl CoA before it can enter the Krebs cycle.
Explanation: Pyruvate is a three carbon compound. Before pyruvate can enter the Krebs cycle, it must be oxidized to acetyl CoA and carbon dioxide. The acetyl CoA then enters the Krebs cycle.
This reaction is an oxidative decarboxylation, an irreversible oxidation process in which the carboxyl group is removed from pyruvate as a molecule of carbon dioxide, and the two remaining carbons become the acetyl group of acetyl CoA.
The overall reaction of oxidation of pyruvate to acetyl CoA is catalyzed by an enzyme known as pyruvate dehydrogenase complex.