Glycolysis steps
Glycolysis consists of two distinct phases: the energy investment phase and the energy harvesting phase (see figure below). In the first phase, glucose is broken down into 2 molecules of fructose 1,6-bisphosphate at the cost of 2 ATP molecules. The second step gives rise to 1 pyruvate molecule, 2 ATP molecules, and 1 NADH molecule per molecule of fructose 1,6-bisphosphate (double products per glucose molecule).
Figure 1: The overall reaction of glycolysis.