Advanced Placement (AP) Biology Practice Exam

What characterizes allosteric inhibition?

1. A regulatory molecule binds to the active site

2. A change in temperature affects enzyme activity

3. A regulatory molecule binds to a second site, causing a conformational change

4. A competitive inhibitor blocks substrate access

The correct answer is: A regulatory molecule binds to a second site, causing a conformational change

Allosteric inhibition is characterized by the binding of a regulatory molecule to a site other than the active site on an enzyme, often referred to as an allosteric site. This binding induces a conformational change in the enzyme's structure, which can either enhance or inhibit the enzyme's activity. In the case of allosteric inhibition, the conformational change reduces the enzyme's ability to facilitate the reaction by altering the shape of the active site or affecting the overall dynamics of the enzyme. This mechanism allows for fine-tuning of metabolic pathways, as allosteric regulators can respond to changes in the cellular environment and modulate enzyme activity in a way that is not solely dependent on the concentration of substrate present. Thus, the critical aspect of allosteric inhibition is the interaction at a secondary site leading to a change in the enzyme's functionality, which directly aligns with the chosen answer.