Cells need to regulate enzymes to control the rate of chemical reactions and ensure that only necessary reactions occur. This regulation is crucial for maintaining cellular efficiency and conserving energy. When enzymes are activated or deactivated based on the availability of substrates or the need for specific products, cells can prevent unnecessary reactions from taking place. This is achieved through mechanisms such as competitive inhibition, where a molecule similar to the substrate competes for the active site, and noncompetitive inhibition, where an allosteric inhibitor binds to a different site on the enzyme, altering its shape and preventing substrate binding. By regulating enzyme activity, cells can optimize their metabolic processes and respond effectively to changing conditions.