MCAT Biological and Biochemical Foundations of Living Systems 2026 – 400 Free Practice Questions to Pass the Exam

Phosphofructokinase-1 (PFK-1) plays a crucial role in the regulation of glycolysis, and its activity is influenced by the binding of various molecules, including ATP. The correct mechanism through which ATP binds to PFK-1 is allosteric regulation.

Allosteric regulation refers to the process where the binding of an effector molecule at a site other than the active site of an enzyme induces a conformational change that affects the enzyme's activity. In the case of PFK-1, ATP serves as an allosteric inhibitor at higher concentrations. When ATP binds to the allosteric site of PFK-1, it stabilizes the enzyme in a less active form, thereby reducing its affinity for fructose 6-phosphate, which is its primary substrate. This feedback mechanism ensures that PFK-1 activity decreases when energy levels are high (indicated by high ATP levels), preventing excessive glycolysis when the cell does not need to produce additional ATP.

In this context, substrate-level phosphorylation refers to a different mechanism of ATP generation that occurs in the glycolysis pathway, where a phosphate group is directly transferred to ADP from a phosphorylated intermediate. Feedback inhibition is a broader concept involving the inhibition