glycolysis which Begins the breakdown of glucose is a series of 10 enzyme catalyzed chemical reactions that can be divided into two main phases in the energy investment phase some ATP energy is used to start the process of glucose oxidation by the end of this phase a sixc carbon molecule glucose has been split into two three carbon molecules of glycer aldhy phosphate the three carbon glycer aldhy phosphate molecules now enter the energy payoff phase chemical bonds are broken and NAD plus picks up electrons and hydrogen ions forming nadh the energy released is used to attach phosphate groups the phosphates are transferred to ADP finally making some ATP this way of making ATP is called substrate level phosphorilation a couple more reaction rearrange the atoms in the three carbon molecules more ATP is generated in the final reaction that yields pyrovate for each glucose molecule broken down during glycolysis a net of two atps are formed along with two nadh molecules