Citric acid cycle
In biochemistry, the Citric Acid Cycle, also called Krebs cycle, Citrate Cycle, Tricarboxylic Acid Cycle or TCA, is a series of chemical reactions of central importance in all living cells that utilize oxygen as part of cellular respiration. In these aerobic organisms, the citric acid cycle is a metabolic pathway that forms part of the break down of carbohydrates, fats and proteins into carbon dioxide and water in order to generate energy.

The Krebs cycle is named after Sir Hans Adolf Krebs (1900-1981), who was awarded the 1953 Nobel Prize in Medicine for its discovery.

The citric acid cycle takes place within the mitochondria in eukaryotes, and within the cytoplasm in prokaryotes.

The citric acid cycle forms part of carbohydrate catabolism, protein catabolism and fat catabolism. All these three processes produce acetyl-CoA, a two-carbon acetyl group bound to coenzyme A. Acetyl-CoA is the main input to the citric acid cycle.