Enzymes: what are they and how do they affect activation energy?

• A. Enzymes are biological catalysts that lower the activation energy of chemical reactions.
• B. Enzymes are inhibitors that raise the activation energy.
• C. Enzymes provide energy to reactions by increasing temperature.
• D. Enzymes are lipids that store energy.

Answer: (A)

Enzymes are biological catalysts that speed up chemical reactions by lowering the activation energy—the energy barrier that must be overcome for reactants to reach the transition state and be converted into products. They do this by binding substrates at the active site in the correct orientation, stabilizing the transition state through interactions with amino acids, and sometimes providing a special microenvironment or participating directly in the chemistry. By offering an easier pathway, enzymes increase the reaction rate without changing the overall energy released or required for the reaction to occur (the free energy change stays the same). They do not supply energy to reactions, they do not store energy as lipids, and they are not inhibitors (which would raise the barrier rather than lower it). Temperature can influence enzyme activity, but higher temperatures risk denaturing the enzyme, so the trick is lowering the activation energy rather than adding heat.