What happens to the enzyme after catalyzing a reaction?

• A. It is consumed in the reaction
• B. It remains unchanged and can catalyze additional reactions
• C. It becomes product
• D. It denatures permanently

Answer: (B)

Enzymes act as catalysts and are not consumed in reactions; after they help convert substrates to products, they remain available to catalyze additional reactions. They bind substrates at the active site to form an enzyme–substrate complex and lower the activation energy, but the enzyme itself is not altered permanently in the process, so it can be reused. The products are released and the enzyme returns to its original form to catalyze more reactions. The ideas that the enzyme is used up, becomes product, or denatures permanently don’t fit normal enzyme function—denaturation would only happen under damaging conditions, not during typical catalysis.