Krebs Cycle and Electron Transport Chain

Describes the specific metabolic pathway within cells to account for oxidation of basic food components (carbohydrates, fat, protein) for energy. The reactions all occur within the mitochondria of the cells.

Acetyl CoA can be formed from glucose metabolism, fatty acid metabolism, or amino acid metabolism. No matter how it was formed, the majority of it goes into the Citric Acid, or Krebs Cycle.

Acetyl CoA splits off a coenzyme A group. This releases bond energy to power the next reaction. The acetyl group couples to oxaloacetate, resulting in the formation of citrate, which then undergoes a series of conversions. The final product of these conversions is oxaloacetate. This allows for incoming Acetyl CoA and the cycle is repeated. The acetyl group is completely oxidised to form 2 carbon dioxide molecules. One of these reactions produces GTP, which is converted to ATP. Four of these reactions are oxidative reactions; 3 where NAD acts as the electron acceptor, and 1 where FAD acts as the electron acceptor. Since the supply of oxidised cofactors is limited, NADH and FADH must be re-oxidised, which is where the electron transport chain comes into play.

The purpose of the electron transport chain is to reoxidise NADH and FADH to NAD and FAD, respectively. This occurs through a series of oxidations/reduction reactions, producing bond energy harnessed to the reaction of the production of ATP and water. 3 ATP are produced for every NADH involved, and 2 ATP are produced for every FADH involved. Oxygen is the final electron acceptor, producing water.