How does competitive inhibitor inhibits the activity of an enzyme? Explain with an example.

Competitive inhibitor inhibits the enzyme activity by binding with its active site so that substrate cannot bind. During this kind of inhibition substrate and inhibitor compete with each other for binding the active site of an enzyme. Both substrate and inhibitor are similar in structure.

For example in Citric acid cycle there is a enzyme succinate dehydrogenase that act on the substrate succinate to convert it into fumarate. Succinate and malonic acid are similar in structure. Malonic acid act as a competitive inhibitor of succinate dehydrogenase. Both malonic acid and succinate compete for the active side of the enzyme which either slow down the reaction or inhibit it depending on the concentration of inhibitor (malonic acid).