Which statement is NOT true about enzymes?

Which statement is NOT true about enzymes?

• A. Enzymes lower activation energy
• B. Enzymes stabilize transition states
• C. Enzymes increase the rate of the reaction
• D. Enzymes change the overall free energy change (ΔG) of the reaction

Answer: (D)

Enzymes speed up reactions by changing how fast the reaction can proceed, not by changing the overall energy charge of the reaction. They lower the activation energy, the energy barrier that must be overcome for reactants to reach the transition state. They do this by providing an active site environment that stabilizes the transition state and properly orients substrates, sometimes using mechanisms like induced fit, acid-base catalysis, covalent catalysis, or metal ion participation. Because of this lowered barrier, a larger fraction of molecules can reach the transition state each moment, so the rate of the reaction increases.

The energy difference between reactants and products, ΔG, is what determines whether a reaction is thermodynamically favorable and how much energy is released or required. Enzymes do not alter this thermodynamic curve; they do not change the final amount of energy difference or the equilibrium position. So while they dramatically speed up how quickly equilibrium is approached, they do not change the overall free energy change of the reaction.

For example, a sugar-hydrolyzing enzyme lowers the barrier to break the glycosidic bond, allowing the reaction to proceed rapidly, but the energy difference between starting sugar and products remains the same as it would without the enzyme. That’s why the statement about changing ΔG is not true, while the others—lowering activation energy, stabilizing the transition state, and increasing the reaction rate—are accurate descriptions of how enzymes work.