Final answer:
Pyruvate dehydrogenase removes a carboxyl group from pyruvate, resulting in the release of carbon dioxide and converting pyruvate into an acetyl group, which when attached to CoA forms acetyl CoA. This occurs twice per glucose molecule. The regulation of pyruvate dehydrogenase is critical for maintaining cellular energy balance.
Step-by-step explanation:
When we consider what happens to each carbon atom in pyruvate during the action of the pyruvate dehydrogenase complex, we must look at the metabolic process known as oxidative decarboxylation. This complex enzyme-driven reaction is critical in the conversion of pyruvate, generated from glycolysis, into acetyl CoA, which is vital for the Citric Acid Cycle also known as the Krebs cycle.
In the first step, pyruvate dehydrogenase removes a carboxyl group from pyruvate, which releases a molecule of carbon dioxide. This steps transforms the three-carbon pyruvate into a two-carbon hydroxyethyl group that remains attached to the enzyme. This decarboxylation reaction signifies the first carbon to be removed from the initial six-carbon glucose molecule that entered glycolysis. As each glucose molecule is broken down into two pyruvate molecules, this decarboxylation step occurs twice, thus releasing two carbon dioxide molecules and leaving behind two hydroxyethyl groups bound to the enzyme.
The subsequent reactions involve the transformation of the hydroxyethyl group into an acetyl group and transfer onto Coenzyme A (CoA) to form acetyl CoA. During this transfer, the enzyme dihydrolipoyl transacetylase assists in the process and the hydroxyethyl group is oxidized to form an acetyl group, a reaction that yields NADH. The resultant molecule, acetyl CoA, is what enters the Krebs cycle, ultimately playing a pivotal role in cellular energy production.
Regulation of pyruvate dehydrogenase is crucial and is influenced by cellular energy needs. The enzyme activity is modulated through accumulations of acetyl groups or NADH, and also by reversible phosphorylation. This ensures that the cell does not overproduce acetyl CoA when the energy supply is adequate.