Which of the following is the first ATP-generating step in glycolysis?

In glycolysis, the first ATP-generating step occurs during the conversion of 1,3-bisphosphoglycerate to 3-phosphoglycerate. This reaction is catalyzed by the enzyme phosphoglycerate kinase during Step 7 of the glycolytic pathway. At this point, the high-energy acyl phosphate bond in 1,3-bisphosphoglycerate is used to transfer a phosphate group to ADP, forming ATP. This step is significant as it marks the first instance where ATP is produced directly in the glycolytic pathway, contributing to the overall energy yield of the process.

In this context, understanding why this step is recognized as the first ATP-generating event is crucial. Glycolysis as a whole involves an initial investment of ATP in the early stages (specifically during Steps 1 and 3) to prepare glucose for subsequent breakdown. However, actual ATP production does not occur until Step 7, distinguishing it as the first moment of net ATP generation in the pathway. The completion of glycolysis ultimately culminates in a net yield of ATP, driven by the energy-rich intermediates formed during earlier steps, especially prior to Step 7.