14. After its synthesis, Acetyl CoA is fed into a cyclic pathway alternately called the citric acid cycle , the TCA (tricarboxylic acid) cycle , or the Krebs cycle (Figure 4). In this cycle the acetyl group on acetyl CoA is oxidized to CO2. Four reactions in the Krebs cycle involve the transfer of a pair of electrons from a substrate to an electron accepting coenzyme. Three of the reactions reduce the coenzme NAD+ to NADH , and one reduces the coenzyme FAD to FADH2 . In addition, a GDP is converted to GTP. The enzymes that carry out these reactions are located in the mitochondrial matrix and at the matrix surface of the inner membrane. The reduced coenzymes (NADH and FADH2) generated in the citric acid cycle store the energy released in glucose oxidation, and synthesis of ATP is then coupled to the reoxidation of these compounds by O2 in a process that involves the electron transport chain . Some of the intermediates in the Krebs cycle are substrates that will be used in the second lab exercise (succinate, malate), so note the position of each these substrates in the cycle and the reducedcoenzymes that are produced from their oxidation.
![Biogénesis mitocondrial ,[object Object],[object Object]](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)