Citric Acid Cycle Research Paper

The Role of the Citric Acid Cycle
The Citric Acid Cycle is a series of enzyme-catalysed reactions that take place in the mitochondrial matrix of all aerobic organisms. It involves the oxidation of the acetyl group of acetyl CoA to two molecules of carbon dioxide. Each cycle produces one molecule of ATP by substrate-level phosphorylation, and reduces three molecules of NAD and one molecule of FAD for use in Oxidative Phosphorylation. The cycle is preceded by Glycolysis, which also occurs in anaerobic respiration, and the pyruvate dehydrogenase complex, which occur in the cytoplasm and the mitochondrial matrix respectively. In aerobic respiration, glycolysis breaks down one molecule of glucose and two molecules of pyruvate, and gives a net product
It serves as a precursor to oxidative phosphorylation, which is where the majority of ATP in respiring animals is produced. It is for this reason that the rapid replenishment of the reactants in the cycle is a vital process if any are removed for biosynthesis. Oxaloacetate, for example, is often converted into amino acids for protein synthesis, meaning the energy requirements of the cell will increase. This means the rate of the citric acid cycle will reduce until a minimum quantity of oxaloacetate is present, as acetyl CoA produced in the pyruvate dehydrogenase complex cannot enter the cycle unless it condenses with oxaloacetate. To increase the amount of oxaloacetate present, pyruvate is carboxylated in the presence of the enzyme pyruvate carboxylase. Although oxaloacetate is recycled on subsequent turns of the citric acid cycle, it must be constantly replenished when it is drawn off as the cycle could not occur without
It produces both NADH and FADH2, which are passed onto the electron transport chain in oxidative phosphorylation, where the majority of ATP in aerobic organisms is produced. It is also a sorce of numerous biosynthetic precursors such as nucleotide bases, proteins, and haem groups. This means the only waste molecule produced by the cycle is CO2, which can be removed with relative ease. The cycle may also act as the entry point into melabolism for any amino acids which may have otherwise gone to waste. These factors mean the citric acid cycle operates at a very high level of efficiency, and must be controlled to a high degree. It acts as the final common pathway for the oxidation of many fuel molecules, and plays a huge role in metabolism as a whole as a result of