Acetyl coenzyme A or acetyl-CoA is an important molecule in metabolism, used in many biochemical reactions. Its main function is to convey the carbon atoms within the acetyl group to the citric acid cycle (Krebs cycle) to be oxidized for energy production. The structure of coenzyme A (CoASH or CoA) consists of a β-mercaptoethylamine group linked to the vitamin pantothenic acid through an amide linkage. The acetyl group (indicated in blue in the structural diagram on the right) of acetyl-CoA is linked by a "high energy" thioester bond to the sulfhydryl substituent of the β-mercaptoethylamine group. It is this thioester bond that makes acetyl-CoA one of the "high energy" compounds. Hydrolysis of the thioester bond is exergonic (-31.5 kJ). Acetyl-CoA is produced during breakdown of carbohydrates through glycolysis, as well as by the beta-oxidation of fatty acids. It then enters the citric acid cycle, where the acetyl group is further oxidized to carbon dioxide and water, with the energy thus released captured in the form of 11 ATP and 1 GTP molecules per acetyl group that enters the cycle.