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Describe the mechanism of feedback inhibition and the role this process plays in controlling enzyme activity.

Feedback inhibition is also known as negative feedback and end-product inhibition. In this mechanism, the product of a particular metabolic pathway inhibits an enzyme that catalyzes a reaction earlier in the pathway. For example, the end-product might be an allosteric inhibitor of that enzyme binding to a location on the enzyme outside the active site. When the allosteric inhibitor binds, it changes the shape of the enzyme and prevents the enzyme from binding to its substrate. This "shuts off" the enzyme, and because the product of one reaction is the substrate for another, it shuts down the pathway. The inhibition is released as the amount of the end-product decreases. When this occurs, the pathway will be turned on again, because the cell again needs the end-product. Therefore, feedback inhibition controls enzyme activity so that energy is not wasted.