Enzymes bind to ________ at the ________.

• A. Substrates; active site (correct)
• B. Substrates; allosteric site
• C. Products; active site
• D. Inhibitors; active site

Answer: (A)

Enzymes catalyze reactions by binding their substrates at the active site, the specially shaped pocket where chemistry happens. The active site binds the substrate through complementary shape and chemical interactions, stabilizing the transition state and lowering the activation energy needed for the reaction. Once the reaction occurs, products are released and the enzyme is ready to bind new substrate molecules. The allosteric site, by contrast, is a separate region used to regulate activity, not to hold substrates for catalysis. Inhibitors can block activity by binding at the active site or elsewhere, but the fundamental binding of the substrate to the active site is what drives the catalytic process.