Cellular respiration begins with the process of glycolysis. Glycolysis is an anaerobic and aerobic pathway and occurs within the cytoplasm of cells. This pathway catalyzes 1 glucose molecule and generates 2 pyruvate molecules, 2 ATP, and 2 NADH. The chemical reaction for glycolysis is Glucose + 2 NAD+ + 2ADP+ 2 PI→ 2 pyruvate + 2 NADH +2 H+ + 2 ATP + 2 H20. The hydroxyl groups in the reaction permit the phosphorylation of the glucose molecule. Hexokinase catalyzes the phosphorylation of 6 carbon molecules, using ATP as the source of the phosphate. This subsequently yields glucose-phosphate, which is a more reactive form of glucose.