Which molecule must be regenerated for glycolysis to continue under anaerobic conditions?

For glycolysis to continue under anaerobic conditions, the regeneration of NAD+ is essential. During glycolysis, glucose is broken down into pyruvate, and in this process, NAD+ is reduced to NADH. If NAD+ is not regenerated, glycolysis cannot proceed because there would be no available NAD+ to accept electrons during the conversion of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate.

Under anaerobic conditions, cells utilize fermentation pathways to regenerate NAD+. In lactic acid fermentation, for instance, pyruvate is reduced to lactate, facilitating the conversion of NADH back to NAD+. In alcoholic fermentation, pyruvate is converted to ethanol and carbon dioxide, similarly regenerating NAD+. This regeneration of NAD+ is crucial for sustaining glycolysis and allowing the production of ATP even in the absence of oxygen.

Oxygen is not required in anaerobic conditions, and while ADP and ATP are involved in the overall process of cellular respiration and energy transfer, they do not directly play a role in the specific regeneration necessary for glycolysis to continue when oxygen is not present.