What coenzyme is important for single-carbon transfer reactions?

Folate, specifically in its active form as tetrahydrofolate (THF), is essential for single-carbon transfer reactions in metabolism. These reactions are crucial for synthesizing amino acids, nucleotides, and other important biomolecules. The structure of folate allows it to carry and donate single-carbon units in various forms, such as formyl, methenyl, methylene, and dimethyl. This functionality is particularly important in the synthesis of purines and thymidine, which are necessary for DNA production and cell division.

In contrast, the other coenzymes listed serve different roles. Thiamine is primarily involved in decarboxylation reactions and carbohydrate metabolism. Pyridoxine (vitamin B6) acts mainly as a coenzyme in amino acid metabolism, facilitating transamination and decarboxylation reactions rather than single-carbon transfers. Biotin is associated with carboxylation reactions, playing a role in the synthesis of fatty acids and gluconeogenesis but does not directly participate in single-carbon transfers.

Thus, folate's specific ability to mediate single-carbon transfers makes it the correct answer for the question regarding the coenzyme important in these reactions.