What compound is formed by the addition of CO2 to acetyl CoA in the first step of fatty acid synthesis?

The correct answer is malonyl-CoA, which is formed when carbon dioxide (CO2) is added to acetyl CoA in the first step of fatty acid synthesis. This reaction is catalyzed by the enzyme acetyl-CoA carboxylase, which facilitates the carboxylation of acetyl CoA. The process involves the incorporation of CO2 into acetyl CoA, resulting in malonyl-CoA, a three-carbon compound that plays a crucial role in the elongation of fatty acid chains.

Malonyl-CoA is essential in fatty acid biosynthesis as it serves as the actual building block for the growing fatty acid chain during the synthesis process. The structure of malonyl-CoA allows it to participate in subsequent condensation reactions, where it donates two-carbon units to extend the fatty acid chain through a series of reactions that ultimately lead to the formation of long-chain saturated fatty acids, such as palmitate.

In summary, malonyl-CoA is generated from the carboxylation of acetyl CoA, setting the stage for further synthetic processes in fatty acid metabolism.