The rate-affecting steps are the slower steps of a reaction and thus determines the rate of the overall reaction. In glycolysis, the rate-affecting steps are coupled with the hydrolysis of ATP or the phosphorylation of ADP to create the highly energetically favorable and irreversible reaction mechanism. This final step is highly regulated and deliberately irreversible because pyruvate is a crucial intermediate building block for further metabolic pathways.[11] Once pyruvate kinase synthesizes pyruvate, pyruvate either enters the TCA cycle for further production of ATP under aerobic conditions, or is reduced to lactate under anaerobic conditions.