How many total ATP molecules are produced during glycolysis?

During glycolysis, a total of four ATP molecules are produced. However, the net gain of ATP is only two because two ATP molecules are utilized in the early steps of glycolysis to help convert glucose into intermediates. The process of glycolysis begins with one glucose molecule and involves a series of enzymatic reactions that ultimately convert glucose into two molecules of pyruvate, producing ATP and NADH in the process.

The four ATP molecules produced come from substrate-level phosphorylation, where ATP is generated directly from the energy released during the conversion of intermediates. The fact that the process requires two ATP at the start is why the net ATP yield is two.

This understanding underscores the importance of glycolysis as the first step in cellular respiration, which sets the stage for further ATP production during the citric acid cycle and oxidative phosphorylation.