What is the net ATP gain from glycolysis?

The net gain of ATP from glycolysis is indeed two ATP molecules. During glycolysis, a six-carbon glucose molecule is broken down into two three-carbon pyruvate molecules. In the initial steps of glycolysis, two ATP molecules are consumed to convert glucose into a more reactive form. Throughout the latter steps of glycolysis, four ATP molecules are produced through substrate-level phosphorylation.

To calculate the net gain, the amount of ATP produced is subtracted from the amount consumed. While four ATP are produced, the two ATP that were used at the beginning results in a net gain of two ATP. This fundamental process highlights the efficiency of glycolysis as it begins the process of cellular respiration, providing energy in the form of ATP even before further energy production occurs in subsequent metabolic pathways.