Final answer:
The enzyme pyruvate decarboxylase catalyzes the removal of a carboxyl group from pyruvic acid, releasing carbon dioxide and forming acetaldehyde. This reaction is involved in the production of ethanol through the fermentation of pyruvic acid by yeast.
Step-by-step explanation:
In the reaction that converts pyruvic acid to acetaldehyde and CO₂, the enzyme pyruvate decarboxylase catalyzes the removal of a carboxyl group from pyruvic acid, releasing carbon dioxide as a gas.
The loss of carbon dioxide reduces the size of the molecule by one carbon, resulting in the formation of acetaldehyde. This reaction plays a key role in the fermentation of pyruvic acid by yeast, which produces ethanol found in alcoholic beverages.