Why Is the Krebs Cycle Called a Cycle?

The Krebs cycle, also known as the citric acid cycle or tricarboxylic acid cycle, is part of a series of chemical reactions that organisms use to break down food into a form of energy that cells can use. The cycle occurs in the mitochondria of cells, using 2 molecules of pyruvic acid from glycolysis to produce the energy molecules. The Krebs cycle forms (per two molecules of pyruvic acid) 2 ATP molecules, 10 NADH molecules, and 2 FADH₂ molecules. NADH and the FADH₂ produced by the cycle are used in the electron transport system.

Why It's a Cycle

The final product of the Krebs cycle is oxaloacetic acid. It is a cycle because oxaloacetic acid (oxaloacetate) is the exact molecule needed to accept an acetyl-CoA molecule and start another turn of the cycle.