Which of the following compounds is formed first in the Citric Acid Cycle?

In the Citric Acid Cycle, the first compound that is formed is citrate. This occurs during the initial step of the cycle when acetyl-CoA, derived from carbohydrates, fats, and proteins, combines with oxaloacetate to form citrate. This reaction is catalyzed by the enzyme citrate synthase.

Citrate is a six-carbon compound that plays a crucial role as the starting point for the cycle, directing the sequence of reactions that will subsequently lead to the extraction of energy through the oxidation of its carbon skeleton. The conversion of acetyl-CoA and oxaloacetate into citrate initiates the metabolism of these substrates, allowing for the continuous cycle of reactions that are responsible for producing reduced cofactors like NADH and FADH2, which are essential for ATP production in the electron transport chain. Thus, understanding that citrate is the first product formed provides a fundamental grasp of the cycle's overall flow and function.