Why Is the Krebs Cycle Called a Cycle?

Citric Acid Cycle

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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.

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Helmenstine, Anne Marie, Ph.D. "Why Is the Krebs Cycle Called a Cycle?" ThoughtCo, Aug. 27, 2020, thoughtco.com/why-is-the-krebs-cycle-608204. Helmenstine, Anne Marie, Ph.D. (2020, August 27). Why Is the Krebs Cycle Called a Cycle? Retrieved from https://www.thoughtco.com/why-is-the-krebs-cycle-608204 Helmenstine, Anne Marie, Ph.D. "Why Is the Krebs Cycle Called a Cycle?" ThoughtCo. https://www.thoughtco.com/why-is-the-krebs-cycle-608204 (accessed May 12, 2021).