Second stage of cellular respiration carried out through the Citric acid cycle/ Krebs cycle/ TCA cycle in which Acetyl Co-A is metabolized to carbon dioxide and water, and reduces co-enzymes that are re-oxidized through the electron transport chain, linked to the generation of ATP. It occurs totally in the mitochondria of a cell. The enzymes of second stage of cellular respiration are located in the mitochondrial matrix either free form or attached to the inner side of the inner mitochondrial membrane. In this stage of cellular respiration, requires oxygen and does not function under anaerobic conditions.
The Citric acid cycle of cellular respiration is the common pathway for oxidation to carbon dioxide and water of glucose, fatty acids, and some amino acids. This oxidation supply energy for the generation of majority of ATP in the body. The major entry into Citric acid cycle is through Acetyl Co-A. Acetyl Co-A is the substrate of Citric acid cycle that arises from the breakdown of glucose, glucogenic amino acids, and fatty acids.
Two carbon atoms enter into the citric acid cycle as Acetyl Co-A and leave as carbon dioxide (CO2). Four pairs of electrons are removed from the substrate; three pairs leave in the form of NADH, and one pair leaves as FADH2. These energy rich molecules, NADH and FADH2 are oxidized in stage III cellular respiration via the electron transport chain for ATP generation. Oxidation of one molecule of Acetyl Co-A via Citric acid cycle gives 12 molecules of ATP. Therefore, large amount of energy is produced in this stage of cellular