Biochemistry Module 2 Practice Test

The main idea is that enzymes lower the energy barrier by using the energy released when the substrate binds to the enzyme. When the substrate fits into the active site, a network of interactions—hydrogen bonds, ionic attractions, van der Waals forces, and desolvation—forms between enzyme and substrate. This binding energy stabilizes the transition state of the reaction, making it easier for bonds to break and new bonds to form. In other words, the enzyme creates a favorable environment and, through binding energy, helps the system reach and pass through the high-energy transition state more readily.

ATP hydrolysis isn’t required for every enzymatic step; some reactions don’t use ATP at all. Thermal energy from the surroundings can influence reaction rates in general, but it isn’t the mechanism by which an enzyme specifically lowers the activation energy. Similarly, energy stored in substrate bonds before binding isn’t the direct source of catalysis once binding occurs—the key factor is the energy released during binding that stabilizes the transition state and lowers the barrier.