Cellular respiration is the oxygen-requiring reactions, occurring in the mitochondrion, that breaks down the end products of glycolysis into carbon dioxide (CO2) and water (H2O), while capturing large amounts of energy as adenosine triphosphate (ATP).
Most cells can metabolize a variety of organic molecules to produce ATP. Virtually, all cells metabolize glucose for energy, at least part of the time. Secondly, glucose metabolism is less complex than the metabolism of most other organic molecules.
The formula for complete glucose metabolism is the opposite of photosynthesis. The products of one, is the reactants of another. The formula for glucose metabolism is as follows:
C6H12O6 + 6O2 6CO2 + 6H2O
There are a few basic steps in glucose metabolism. The first stage, glycolysis, does not require oxygen and proceeds in exactly the same way under both aerobic (with oxygen) and anaerobic (without oxygen) conditions.
Glycolysis splits apart a six glucose molecule (six carbon sugar) into three-carbon molecules of pyruvate. The presence of oxygen becomes an issue only in the processes that follow glycolysis. During glycolysis, two ATP molecules are produced. Also, under anaerobic conditions, the pyruvate is usually converted by fermentation into lactate or ethanol.
Cellular respiration is a series of reactions, occurring under aerobic conditions, in which large amounts of ATP are produces. During cellular respiration, the pyruvate produced by glycolysis is broken down to CO2 and H2O. The final reactions of cellular respiration require oxygen because oxygen acts as the final acceptor of electrons.
The two molecules of pyruvate produced by glycolysis are transported across both mitochondrial membranes and into the matrix. Once inside the matrix, pyruvate reacts with a molecule called coenzyme A. Each pyruvate is then split into CO2 and a two carbon molecule called an acetyl group, which immediately attaches to coenzyme A, forming acetyl CoA.
Next, the stages of the reaction form a cyclic pathway known as the Krebs Cycle. Each turn creates one ATP. Since it's happening twice, then there are two as a result of Krebs.
Now, combined with the two ATP from glycolysis, there are four ATP molecules. With thirty-two ATP left to make, the energetic electrons produced by the Krebs Cycle are carried to the electron transport system in the inner mitochondrial membrane.
By now, lying in wait, many energy carriers are ready to go to work. The cell has captured many energetic electrons in carrier molecules: two NADH during glycolysis plus eight more NADH and FADH2 from the matrix reactions, for a total of ten NADH and two FADH2.
The carriers deposit their electrons in the electron transport system located in the inner mitochondrial membrane. Here, their energy is used to generate a hydrogen ion gradient across the inner membrane. The movement of hydrogen ions down through ATPase, their gradient,...