Final answer:
The cofactor that picks up the acetyl group from pyruvate to form acetyl CoA is coenzyme A (CoA), derived from vitamin B5 and necessary for the transition reaction before entering the Krebs cycle.
Step-by-step explanation:
The cofactor that acts as a carrier compound to pick up the acetyl group from the decarboxylation of a pyruvate molecule is coenzyme A (CoA), which is derived from vitamin B5. This reaction takes place in the transition reaction or the bridge reaction where pyruvate, produced from glycolysis, is decarboxylated by the pyruvate dehydrogenase enzyme complex. Here, acetyl CoA is produced allowing the acetyl group to enter the Krebs cycle for further oxidation. Hence, when glycine becomes acetylated within the cellular metabolism context, the relevant cofactor is CoA.