Final answer:
The statement is true; a competitive inhibitor and the substrate cannot bind to the enzyme at the same time because they compete for the same active site.
Step-by-step explanation:
The statement that a competitive inhibitor and the substrate cannot both bind to the enzyme at the same time is true. Competitive inhibition occurs when an inhibitor reversibly binds at the active site of an enzyme, where it competes with the substrate for binding. Because both the competitive inhibitor and the substrate cannot be bound to the active site simultaneously, the presence of a competitive inhibitor can slow the rate of reaction.
However, increasing the concentration of the substrate can overcome this inhibition as the substrate outcompetes the inhibitor for the active site. In contrast, a noncompetitive inhibitor binds to a different site on the enzyme, altering its conformation and affecting the catalysis without directly competing with the substrate for the active site. Therefore, adding more substrate does not reverse the inhibitory effect of a noncompetitive inhibitor.