Glucose is oxidized and O 2 is reduced. Buildup of ATP is an endergonic reaction that requires energy. Rapid breakdown of glucose would lose most energy as nonusable heat. Each metabolic reaction in cellular respiration is catalyzed by its own enzyme.
Glycolysis is the breakdown of glucose to two molecules of pyruvate.
Glycolysis takes place outside the mitochondria and does not utilize oxygen. Produces two immediate ATP molecules per glucose molecule. Electrons pass from higher to lower energy states, energy is released and stored for ATP production. Pyruvate is a pivotal metabolite in cellular respiration. If O 2 is not available to the cell, fermentation, an anaerobic process, occurs.