English: Differences in glycolysis pathways between normal cells and cancer cells. (A) In the presence of oxygen, normal cells produce carbon dioxide up to 38 ATPs per glucose molecule through glycolysis, TCA cycle, and electron transport system. In a hypoxic environment, pyruvates are accumulated without going through the TCA cycle. These accumulated pyruvates in the muscle tissue are converted to lactic acid and only produce 2 ATPs. (B) Cancer cells only use the glycolysis process, regardless of the presence or absence of oxygen; 2 ATPs are produced per glucose molecule and, therefore, compared to normal cells, more glucose is required to obtain energy.