When a metabolic pathway has produced enough end product it can be temporarily shut down by feedback inhibition. The end product binds to the first enzyme in the pathway. This inhibits the first reaction and thus all subsequent reactions. The end product is no longer made. In some pathways, the end product binds to the enzyme’s active site, blocking binding by the first substrate. In other pathways, the end product binds to an allosteric site, away from the active site. This causes a change in the enzyme’s shape, once again blocking the active site. As the end product is used up by the cell, it is no longer available to bind with the enzyme and the pathway resumes normal operation.

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