Advanced Placement (AP) Biology Practice Exam

Which substance acts as a competitive inhibitor of ethyl alcohol in enzyme activity?

1. Formaldehyde

2. Acetaldehyde

3. Isopropanol

4. Methyl alcohol

The correct answer is: Methyl alcohol

The correct answer is that methyl alcohol acts as a competitive inhibitor of ethyl alcohol in enzyme activity. In the context of enzyme-catalyzed reactions, a competitive inhibitor resembles the substrate and competes for binding at the active site of the enzyme. Methyl alcohol, also known as methanol, competes with ethyl alcohol (ethanol) for the active site of alcohol dehydrogenase, the enzyme responsible for the oxidation of alcohols. When methanol binds to the active site, it inhibits the enzyme’s ability to convert ethanol into acetaldehyde, thereby reducing the rate of ethanol metabolism. This is particularly important in toxicology; methanol can cause toxicity by inhibiting the metabolism of ethanol, a safer alcohol, thus leading to the accumulation of toxic metabolites. Understanding the role of methyl alcohol as a competitive inhibitor is crucial in contexts such as alcohol poisoning treatment, where ethanol is often administered to outcompete methanol for the enzyme’s active site and to prevent the formation of toxic metabolites.