Glycolysis is the first step in both aerobic and anaerobic cellular respiration, it will occur in the cytoplasm of the cell with or without the presence of oxygen. The only difference is that in aerobic glycolysis pyruvate is produced, while lactic acid is produced in anaerobic glycolysis. A well-known pathway of glycolysis is the Embden-Meyerhof-Parnas (EMP pathway).1
The overall process of aerobic glycolysis is the conversion of one glucose molecule (C6H12O6) to two molecules of pyruvate, additionally producing 2 ATP. Glycolysis has two main stages: ‘Preparatory Phase’ and ‘Pay Off Phase’ which are completed in 10 enzymatic reactions.2 The Preparatory Phase is reactions where 2 ATP units are consumed for conversion of glucose to two three-carbon sugar phosphates. The Pay Off Phase is where 4 ATP molecules are generated from the transformation of the two three-carbon sugar phosphates to two pyruvates – the net gain is 2 ATP for every glucose molecule. After, the pyruvates undergo Krebs cycle, oxidative phosphorylation to produce the final total of 38 ATP per glucose.
In anaerobic glycolysis, glucose is converted to two units of pyruvate and 2ATP. However, without sufficient oxygen the pyruvates are converted to lactic acid by lactate dehydrogenase – process called fermentation. There are two types of fermentation: Homolactic and Heterolactic. In Homolactic fermentation the final products are two molecules of lactic acid, however in Heterolactic fermentation the final products are carbon dioxide and ethanol.3
2 Nelson, D.L., & Cox, M.M. Lehninger Principles of Biochemistry, 4th Edition.