Written by Merel Dagher (PEACE Advisor)
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The correct answer is c. Feedback inhibition is where the product of a reaction feeds back and inhibits an enzyme responsible for one of the initial steps of the reaction. This can be seen in the process of glycolysis, where the activity of phosphofructokinase is inhibited when the levels of pyruvate get too high. In negative feedback of estrogen production, high levels of estrogen feedback and prevent the synthesis of GnRH, LS and/or FSH. In competitive inhibition, another molecule which resembles the substrate binds to the enzyme, preventing the substrate itself from binding. In noncompetitive inhibition, another molecule binds elsewhere on the enzyme, changing the shape of the active site and preventing the substrate from binding. In allosteric regulation, an enzyme can either be shifted to its active state by an allosteric activator or its inactive state by an allosteric inhibitor. Cooperativity is a form of allosteric regulation that can amply enzymatic activity; the binding of a substrate to one active site stabilizes the active conformation of all other subunits.