Which molecule is regenerated during fermentation to allow glycolysis to continue?

During fermentation, the regeneration of NAD+ is crucial for the continuation of glycolysis. Glycolysis is the metabolic pathway that breaks down glucose to produce pyruvate, yielding a small amount of ATP and NADH in the process. However, for glycolysis to persist, the limited pool of NAD+ needs to be replenished, as it acts as an electron carrier.

In the absence of oxygen, organisms turn to fermentation to allow glycolysis to continue operating. During this anaerobic process, NADH produced in glycolysis is oxidized back to NAD+ through the conversion of pyruvate into either lactic acid (in lactic acid fermentation) or ethanol and carbon dioxide (in alcoholic fermentation). This recycling of NAD+ is vital because it enables glycolysis to produce ATP continuously even without the electron transport chain, which relies on oxygen.

The other molecules listed do not play a role in this specific regeneration during fermentation. FADH2 is involved in other pathways, ATP is a product of glycolysis but not regenerated directly through fermentation, and Acetyl-CoA is a metabolite that feeds into the citric acid cycle when oxygen is present, rather than being involved in anaerobic processes.