Glycolysis requires an initial energy investment of two ATP molecules. In the overall process of glycolysis, one glucose molecule is broken up into two pyruvate molecules with a net return of two ATP molecules.
Glycolysis is a ten step-pathway that is universally performed by all living organisms. The first stage of glycolysis, the energy investment phase, requires one glucose and two molecules of ATP. In this stage, the original glucose molecule is split into two three-carbon molecules. The second stage of glycolysis, the energy payoff phase, converts the two three-carbon molecules of glyceraldehyde phosphate into two pyruvate molecules. In the second stage, four molecules of ATP and two molecules of NADH are released.