ACS Biochemistry Practice Exam

In the glycolysis pathway, the step that produces NADH occurs during the conversion of glyceraldehyde-3-phosphate (G3P) to 1,3-bisphosphoglycerate (1,3-BPG). This reaction is catalyzed by the enzyme glyceraldehyde-3-phosphate dehydrogenase.

During this reaction, a hydrogen atom (with its electrons) is transferred from G3P to NAD+, reducing it to NADH. This is a crucial step in glycolysis because NADH plays an important role in cellular respiration, transporting electrons to the electron transport chain for ATP production.

1,3-bisphosphoglycerate is formed as a product of this reaction, and it possesses a high-energy phosphate bond, which is subsequently used in the next step of glycolysis to generate ATP. This is a clear identification of the step where NADH is generated, substantiating why 1,3-bisphosphoglycerate is the correct answer. The other options do not directly relate to the NADH-producing step of glycolysis, making them unrelated to this specific question.