Under anaerobic conditions, which molecule is predominantly produced from pyruvate?

• A. Lactate
• B. Acetyl-CoA
• C. Pyruvate
• D. Ethanol

Answer: (A)

Regenerating NAD+ to keep glycolysis going when oxygen is scarce is accomplished by converting pyruvate to lactate in the cytosol. This lactate dehydrogenase reaction replenishes NAD+ from NADH, allowing glycolysis to continue producing ATP without oxidative phosphorylation. Acetyl-CoA formation from pyruvate requires pyruvate dehydrogenase and feeds into the mitochondria and the aerobic pathways, which isn’t favored without oxygen. Pyruvate is the substrate here, not the end product, and ethanol production via fermentation occurs in certain microbes like yeast, not typically in human tissues under anaerobic stress. Therefore, lactate is the predominant product from pyruvate under anaerobic conditions.