Advanced Placement (AP) Biology Practice Exam

What happens during allosteric activation of an enzyme?

1. The enzyme becomes permanently active.

2. The active site becomes available when a regulatory molecule binds to a different site.

3. The enzyme loses its ability to bind substrates.

4. The regulatory molecule directly binds to the active site.

The correct answer is: The active site becomes available when a regulatory molecule binds to a different site.

During allosteric activation of an enzyme, the binding of a regulatory molecule to a site other than the active site, known as the allosteric site, induces a conformational change in the enzyme. This change often enhances the enzyme's catalytic activity by making the active site more accessible or better suited for substrate binding. Because the regulatory molecule binds at a distinct site, this interaction can stabilize the enzyme in a form that has a higher affinity for the substrate or can facilitate the transition state, thus promoting the enzymatic reaction. This mechanism illustrates the importance of enzyme regulation and showcases how metabolic pathways are finely tuned through allosteric interactions. Allosteric activation is dynamic and reversible, allowing for a rapid response to changes in cellular conditions or concentrations of metabolites. This differs significantly from options suggesting permanence or loss of function, as those do not accurately represent the nature of allosteric regulation.