Question

Conversion of pyruvic acid into ethyl alcohol is mediated by

• A. Phosphatase.
• B. Dehydrogenase.
• C. Decarboxylase and dehydrogenase.
• D. Catalase.

Answer 1

Answer: (C)

Decarboxylase and dehydrogenase.

Fermentation is a metabolic process that converts sugar to acids, gases, or alcohol and is carried out by a wide range of organisms. Yeast and other microorganisms ferment glucose to ethanol and CO${}_2$, rather than to lactate as in muscles of higher vertebrates. Glucose is converted to pyruvate by glycolysis, and the pyruvate is converted to ethanol and CO${}_2$ in a two-step process:
In the first step, pyruvate is decarboxylated in an irreversible reaction catalyzed by pyruvate decarboxylase. Pyruvate decarboxylase requires Mg${}^{2+}$ and has a tightly bound coenzyme, thiamine pyrophosphate.
In the second step, acetaldehyde is reduced to ethanol through the action of alcohol dehydrogenase, with the reducing power furnished by NADH derived from the dehydrogenation of glyceraldehyde 3-phosphate.
Ethanol and CO${}_2$ are thus the end products of ethanol fermentation, and the overall equation is as follows:
Glucose + 2ADP + 2Pi ----> 2 ethanol + 2 CO${}_2$ + 2 ATP + 2 H${}_2$O