A student investigates the effect of a competitive inhibitor on the rate of an enzyme-controlled reaction. The student finds that increasing the substrate concentration eventually restores the original maximum rate of reaction. Explain why increasing substrate concentration overcomes competitive inhibition.

Competitive inhibitors have a structure similar to the substrate and bind to the active site of the enzyme. The binding is reversible, so the inhibitor can dissociate. When substrate concentration is increased, more substrate molecules are available to compete for the active site. At sufficiently high substrate concentrations, the probability that a substrate molecule occupies the active site is much greater than that of the inhibitor, so the enzyme is largely free to catalyse the reaction. Consequently the maximum rate (Vmax) is restored.