Glycolysis is the splitting up of the sugar, and it is a common step in both aerobic and anaerobic respiration. It is the only process in respiration in an anaerobic organism. Glycolysis is the process of partial oxidation of glucose to form two molecules of pyruvic acid, and it does not require oxygen. In glycolysis, with the help of enzyme hexokinase, glucose is phosphorylated to glucose-6-phosphate by ATP. The glucose-6-phosphate isomerase to fructose-6-phosphate by the action of enzyme phosphohexoisomerase. To form fructose-1,6-biphosphate, the fructose-6-phosphate is phosphorylated. The transfer of phosphate from ATP to fructose-6-phosphate is mediated by phosphofructokinase, which is a rate-limiting enzyme.