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 that would waste resources. Competitive inhibition occurs when a molecule similar to the substrate competes for the active site, blocking the substrate from binding. Noncompetitive inhibition involves an allosteric inhibitor binding to a different site on the enzyme, altering its shape and preventing substrate binding. Both mechanisms are vital for cellular regulation and energy conservation.