Cell Respiration

During cell respiration food materials are oxidized to carbon dioxide and water in the presence of oxygen. One of the most important fuels is glucose. The overall equation for cell respiration in the presence of oxygen is:

        C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy

Under aerobic condition glucose metabolism takes place in four stages, glycolysis, pyruvic acid oxidation, Kerbs citric acid cycle and oxidative phosphorylation in the hydrogen/electron transfer system.



(1) Glycolysis. The breakdown of glucose to pyruvic acid is called glycolysis. Glycolysis can take place in the absence of oxygen (anaerobic condition) or in the presence of oxygen (aerobic condition). The enzymes for glycolysis are found in the soluble faction of the cell, outside the mitochondria.

(2) Pyruvic and oxidation. Under aerobic conditions the pyruvic acid molecule is metabolized to a molecule of acetyle coenzyme A (acetyl CoA).

(3) Krebs citric acid cycle. Each acetyl CoA molecule condenses with a molecule of oxalacetic acid to produce a molecule of citric acid. After several steps oxaloacetic acid is regenerated. Krebs cycle are located in the matrix of the mitochondrion.

(4) Oxidative phoshporylation in the hydrogen transfer system. Several pairs of hydrogen atoms are released during glycolysis, pyruvic acid oxidation and the Kerbs cycle. These are passed through the election transfer system, and are finally accepted by molecular oxygen. During this process ADP is phosphorylated to ATP with inorganic phosphate. The enzymes of the hydrogen transport system are located in the inner membrane of the mitochondrion.