Which molecule initiates the Citric Acid Cycle?

The initiation of the Citric Acid Cycle, also known as the Krebs cycle or TCA cycle, begins with the combination of Acetyl CoA and oxaloacetate to form citrate. Acetyl CoA serves as the primary input molecule that feeds into the cycle.

Acetyl CoA is produced from various metabolic pathways, including glycolysis and fatty acid oxidation. When it enters the Citric Acid Cycle, it combines with oxaloacetate, which is a four-carbon molecule. This reaction is catalyzed by the enzyme citrate synthase, resulting in the formation of citrate, a six-carbon compound.

This process is crucial because it transforms the chemical energy stored in Acetyl CoA into a series of reactions that ultimately lead to ATP production and the reduction equivalents needed for ATP synthesis through oxidative phosphorylation. The significance of Acetyl CoA as the initiator lies in its central role in metabolism, making it a key player in linking carbohydrate, fat, and protein metabolism.

This understanding emphasizes the importance of Acetyl CoA in the energy production pathway within the cell.