THE CITRIC ACID CYCLE
The citric acid cycle is an eight-step process that begins and ends with the same molecule: four-carbon oxaloacetate; hence, the process goes through a cycle. The name "citric acid cycle" comes from the fact that citric acid, or citrate, is produced in the first step, when oxaloacetate combines with a two-carbon acetyl group from acetyl-CoA.

Two turns of the citric acid cycle are needed to process the two molecules of acetyl-CoA formed from the original glucose molecule. A total of four molecules of CO₂ are given off, and the hydrogen atoms removed are used to form six NADH and two FADH₂, both of which are used later. Also, a small amount of ATP is produced: two molecules.