Which statement best describes the role of vitamins as coenzymes in metabolism, with an example involving thiamine pyrophosphate (TPP) in pyruvate dehydrogenase?

Which statement best describes the role of vitamins as coenzymes in metabolism, with an example involving thiamine pyrophosphate (TPP) in pyruvate dehydrogenase?

• A. Thiamine pyrophosphate (TPP) is a cofactor for decarboxylation in pyruvate dehydrogenase.
• B. Vitamin C acts as a cofactor for NAD+ synthesis.
• C. Folic acid acts as a cofactor for carboxylation in metabolism.
• D. Vitamin A serves as a coenzyme in glycolysis.

Answer: (A)

Vitamins often serve as cofactors that enable enzymes to carry out reactions in metabolism. Thiamine is converted to thiamine pyrophosphate, a cofactor that attaches to the pyruvate dehydrogenase complex and drives decarboxylation of pyruvate. This step removes a carbon dioxide from pyruvate and forms a reactive intermediate on the thiazolium ring of TPP. That intermediate is then transferred through the rest of the complex to ultimately form acetyl-CoA, which feeds the acetyl group into the citric acid cycle. This is why the statement identifying TPP as a cofactor for decarboxylation in pyruvate dehydrogenase is correct. The other options misattribute roles: vitamin C isn’t a cofactor for NAD+ synthesis; folic acid mainly participates in one-carbon transfer reactions rather than carboxylation; and vitamin A does not act as a coenzyme in glycolysis.

Vitamins often serve as cofactors that enable enzymes to carry out reactions in metabolism. Thiamine is converted to thiamine pyrophosphate, a cofactor that attaches to the pyruvate dehydrogenase complex and drives decarboxylation of pyruvate. This step removes a carbon dioxide from pyruvate and forms a reactive intermediate on the thiazolium ring of TPP. That intermediate is then transferred through the rest of the complex to ultimately form acetyl-CoA, which feeds the acetyl group into the citric acid cycle. This is why the statement identifying TPP as a cofactor for decarboxylation in pyruvate dehydrogenase is correct.

The other options misattribute roles: vitamin C isn’t a cofactor for NAD+ synthesis; folic acid mainly participates in one-carbon transfer reactions rather than carboxylation; and vitamin A does not act as a coenzyme in glycolysis.