Answer to Question #99757 in Chemistry for ohaniso

Question

why yeast might produce ethanol during fermentation if ethanol is eventually toxic to them.

Answer 1

Fermentation in yeasts starts with the glycolysis - transformation of glucose to two pyruvate molecules. Under the anaerobic conditions, pyruvate cannot be involved in the citric acid cycle. As a result, glycolysis is the only way to produce ATP - a metabolic source of energy. However, the process of glycolysis requires the presence of NAD⁺. One of the possibilities to oxidize NADH to NAD⁺ is to reduce pyruvate to ethanol. The process leads to the production of ethanol, carbon dioxide, and NAD⁺ molecules that can be used in glycolysis. Although ethanol is toxic for yeasts, they can survive in the solution containing up to 14% ethanol.