Final answer:
Acetyl coenzyme A (acetyl CoA) is the molecule that conveys 2 carbons from pyruvate to the Krebs cycle through an oxidative decarboxylation reaction catalyzed by pyruvate dehydrogenase.
Step-by-step explanation:
The molecule responsible for conveying 2 carbons from pyruvate to the Krebs cycle is acetyl coenzyme A (acetyl CoA). During this process, the three-carbon pyruvate generated in glycolysis is transported into the mitochondrial matrix where it undergoes an oxidative decarboxylationreaction catalyzed by the enzyme pyruvate dehydrogenase. This reaction results in the release of one carbon dioxide molecule and the formation of acetyl CoA, a two-carbon molecule. The electrons from this reaction are transferred to NAD+, forming NADH. The acetyl CoA then combines with oxaloacetate to enter the Krebs cycle.