Glycolysis is a 10 step enzyme catalyzed reaction where glucose is broken down into pyruvate, producing ATP. There are two types of glycolysis: aerobic and anaerobic. Aerobic glycolysis occurs in the presence of oxygen while anaerobic glycolysis does not require oxygen. Glycolysis indirectly produces 8 molecules of ATP through the production of 2 molecules of NADH during the reaction, which each produce 3 ATP, for a total net gain of 8 ATP.