Final answer:
Pyruvate undergoes oxidative decarboxylation to be converted into acetyl CoA before entering the citric acid cycle, releasing a carbon as CO2 and producing NADH in the process. The correct answer is D) oxidative decarboxylation.
Step-by-step explanation:
As pyruvate is prepared for the citric acid cycle, it undergoes a process of oxidative decarboxylation. This transformation occurs when the three-carbon pyruvate molecule from glycolysis is converted by the enzyme pyruvate dehydrogenase into a two-carbon acetyl coenzyme A (acetyl CoA) molecule in the mitochondrial matrix. During this reaction, one carbon is removed as carbon dioxide (CO2), and the remaining two-carbon fragment, now called an 'acetyl' group, is attached to coenzyme A (CoA), forming acetyl CoA.
The process is called oxidative because electrons are transferred to NAD* to form NADH, indicating that oxidation is occurring. Furthermore, the removal of a carbon as CO2 represents the 'decarboxylation' part of the reaction. Therefore, the correct answer to the student's question is D) oxidative decarboxylation. This step serves as a vital link between glycolysis and the citric acid cycle, also known as the Krebs cycle, where acetyl CoA is further oxidized for energy production.