Which enzyme catalyzes the carboxylation of acetyl-CoA to malonyl-CoA, and what cofactor is essential for the reaction?

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Multiple Choice

Which enzyme catalyzes the carboxylation of acetyl-CoA to malonyl-CoA, and what cofactor is essential for the reaction?

The main concept here is the enzyme that adds a carboxyl group to acetyl-CoA to form malonyl-CoA, a key step in initiating fatty acid synthesis, and the essential cofactor that enables this carboxylation. Acetyl-CoA carboxylase is the enzyme that performs this reaction, using ATP to activate CO2 and biotin to carry the carboxyl group to acetyl-CoA, producing malonyl-CoA. This downstream product is the substrate for the fatty acid synthase complex, marking the committed step of fatty acid biosynthesis. Biotin acts as the CO2 carrier in this carboxylation process. Other enzymes in the options either modify different substrates or perform different roles: fatty acid synthase carries out the elongation steps after malonyl-CoA is formed; pyruvate carboxylase carboxylates pyruvate to oxaloacetate (not acetyl-CoA); malonyl-CoA decarboxylase removes the carboxyl group from malonyl-CoA. All of them can be biotin-dependent in their own contexts, but the specific carboxylation of acetyl-CoA to malonyl-CoA is the task of acetyl-CoA carboxylase.

The main concept here is the enzyme that adds a carboxyl group to acetyl-CoA to form malonyl-CoA, a key step in initiating fatty acid synthesis, and the essential cofactor that enables this carboxylation. Acetyl-CoA carboxylase is the enzyme that performs this reaction, using ATP to activate CO2 and biotin to carry the carboxyl group to acetyl-CoA, producing malonyl-CoA. This downstream product is the substrate for the fatty acid synthase complex, marking the committed step of fatty acid biosynthesis. Biotin acts as the CO2 carrier in this carboxylation process.

Other enzymes in the options either modify different substrates or perform different roles: fatty acid synthase carries out the elongation steps after malonyl-CoA is formed; pyruvate carboxylase carboxylates pyruvate to oxaloacetate (not acetyl-CoA); malonyl-CoA decarboxylase removes the carboxyl group from malonyl-CoA. All of them can be biotin-dependent in their own contexts, but the specific carboxylation of acetyl-CoA to malonyl-CoA is the task of acetyl-CoA carboxylase.

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