Preparatory phase: In this initial stage, a 6-carbon sugar molecule (usually glucose) is phosphorylated twice to form fructose-1,6-bisphosphate. This process requires the input of 2 ATP molecules and utilizes the enzymes hexokinase and phosphofructokinase.
Cleavage phase: During this stage, fructose-1,6-bisphosphate is cleaved into two 3-carbon sugars: glyceraldehyde-3-phosphate (GAP) and dihydroxyacetone phosphate (DHAP). These 2 molecules are interconvertible, and they both can proceed further in the pathway.
Payoff phase: This final stage involves the conversion of GAP and DHAP into pyruvate, generating ATP and NADH in the process. This stage consists of several enzymatic steps, including substrate-level phosphorylation and oxidation reactions. Ultimately, 2 pyruvate molecules are produced along with a total of 4 ATP and 2 NADH molecules for each molecule of glucose that enters glycolysis.