The aerobic system breaks down glycogen, glucose and fats to provide energy via coupled reactions. It uses oxygen to completely break down 1 mole of glucose into water and carbon dioxide. This occurs in 3 stages:
1. Aerobic glycolysis
2. Kreb's cycle
3. Electron transport chain
Stage 1: Aerobic Glycolysis
The enzyme phosphofructokinase (PFK) initiates the partial breakdown of glucose into pyruvic acid. The presence of oxygen inhibits the accumulation of lactic acid by diverting the pyruvic acid further into the aerobic system. Pyruvic acid combines with coenzyme A to form Acetyl CoA.