As a result of glycolysis, pyruvate oxidation and the citric acid cycle, only a small portion of the energy of glucose has been converted to ATP. At this point, the majority of the usable energy is contained in:

Oxidative phosphorylation produces the majority of the energy generated in the cell. The combination of glycolysis and the citric acid cycle alone yield only 4 ATP. The majority of the energy is stored in the electron carriers NADH and FADH₂. Oxidative phosphorylation can produce 3 ATP for each NADH and 2 ATP for each FADH₂.