The Link to Oxygen

The Link to Oxygen

The citric acid cycle is considered part of aerobic metabolism, but we have not encountered any reactions in which oxygen takes part. The reactions of the citric acid cycle are intimately related to those of electron transport and oxidative phosphorylation, which do eventually lead to oxygen. The citric acid cycle provides a vital link between the chemical energy of nutrients and the chemical energy of ATP. Many molecules of ATP can be generated as a result of coupling to oxygen, and we shall see that the number depends on the NADH and FADH₂ generated in the citric acid cycle.

Recall the classic equation for the aerobic oxidation of glucose:

Glucose + 6O₂ - > 6H₂O + 6CO₂

We have seen the metabolism of glucose through glycolysis. Now we see where the CO₂ comes from—namely, the three decarboxylation reactions associated with the citric acid cycle.

Summary

The citric acid cycle is considered part of aerobic metabolism because of the link to the electron transport chain and oxidative phosphorylation. NADH and FADH₂ generated by the citric acid cycle ultimately pass their electrons to oxygen.