During the second half of glycolysis, the two three-carbon sugar molecules produced in the first half undergo a series of reactions that extract energy. Specifically:

• Glyceraldehyde-3-phosphate is oxidized, and high-energy electrons are transferred to NAD+, forming NADH. This step also adds a second phosphate group to the sugar without using ATP, producing 1,3-bisphosphoglycerate.
• Substrate-level phosphorylation occurs twice: 1,3-bisphosphoglycerate donates a phosphate to ADP, forming ATP and 3-phosphoglycerate; later, phosphoenolpyruvate donates a phosphate to ADP, producing another ATP and pyruvate.
• Additional steps involve rearranging and dehydrating the molecules to increase their energy potential before the final ATP-producing step.

Overall, the second half of glycolysis produces four ATP molecules and two NADH molecules per glucose, resulting in a net gain of two ATP since two were used in the first half

. In summary, during the second half of glycolysis, ATP is made, NADH is produced, and pyruvate is formed from the three-carbon sugars