Enzymes lower the activation energy of a reaction by which mechanism?

• A. Increasing entropy
• B. Lowering the energy of the products
• C. Increasing the free energy
• D. Lowering the activation energy

Answer: (D)

Enzymes speed reactions by stabilizing the transition state, creating a lower-energy path from reactants to products. The activation energy is the energy barrier that must be overcome to reach the transition state; in the active site, enzymes position substrates precisely, provide a favorable microenvironment, and use catalytic groups to stabilize charges or transfer protons, all of which lower the energy required to reach that high-energy state. This lowers the rate-determining barrier without changing the overall energy difference between reactants and products, so the products’ energy remains the same as in an uncatalyzed reaction. Because rate depends exponentially on activation energy, even a small reduction can dramatically speed up the reaction. So the mechanism is lowering the activation energy.