Question

For the formation of ethanol, pyruvic acid is first changed to acetaldehyde by the enzyme
A) Pyruvate dehydrogenase
B) Pyruvate decarboxylase
C) Alcohol oxidase
D) Alcohol dehydrogenase

Answer 1

Hint: Ethanol is an organic chemical compound and simple alcohol. Alcoholic fermentation uses the conversion of pyruvic acid to ethanol to release energy.

Complete Answer:
1) Pyruvate dehydrogenase is an enzyme that catalyses pyruvate and lipoamide reactions to produce the acetylated dihydrolipoamide and carbon dioxide. Usually Pyruvate dehydrogenase is found as a component E1 of pyruvate dehydrogenase complex (PDC). Pyruvate dehydrogenase complex (PDC) is a three-enzyme complex that transforms pyruvate to acetyl-CoA through a process called pyruvate decarboxylation.

2) Pyruvate decarboxylase is a homotetrameric enzyme. Within the cytoplasm, this enzyme converts the decarboxylation of pyruvic acid into acetaldehyde and carbon dioxide. Alcoholic fermentation is used to transform pyruvic acid to ethanol for the release of energy. This is unfinished oxidation wherein aldehyde will be first formed as an intermediate that would then be further oxidised to alcohol. Pyruvate decarboxylase which releases carbon dioxide converts the Pyruvic acid to acetaldehyde conversion.

3) Alcohol oxidase catalyzes the chemical reaction. The substrates of the enzyme are primary alcohol and oxygen. The final products are aldehyde and hydrogen peroxide. This enzyme is also described as ethanol oxidase.

4) Alcohol dehydrogenase (ADH) belongs to a group of dehydrogenase enzymes. It occurs in many species to promote the interaction between alcohols and aldehydes or ketones. It gets reduced by nicotinamide adenine dinucleotide (NAD+) to NADH.

So, the correct answer is B.

Note: Pyruvic acid is an organic acid that is likely to exist in all living cells. It ionises to give a hydrogen ion and an anion called pyruvate. Biochemists use words pyruvate and pyruvate quite interchangeably.