In a chemical reaction catalyzed by an enzyme, the a) products bind to the enzyme active site and increase the activation energy b) products become substrates and the enzyme reacts at the active site c) activation energy is increased when the enzyme reacts with the substrate d) substrate binds to the enzyme’s active site
The correct answer and explanation is:
Correct Answer: d) substrate binds to the enzyme’s active site
In a chemical reaction catalyzed by an enzyme, the substrate binds to the enzyme’s active site. The active site is a specially shaped region of the enzyme that matches the shape of the substrate. This specific interaction is often described by the “lock and key” model or the “induced fit” model. In the lock and key model, the enzyme’s active site and the substrate fit together perfectly. In the induced fit model, the enzyme slightly changes shape to accommodate the substrate when it binds.
The binding of the substrate to the active site forms an enzyme-substrate complex. This complex helps lower the activation energy needed for the reaction to proceed. Activation energy is the minimum amount of energy needed to start a chemical reaction. By lowering this barrier, enzymes make reactions happen faster and more efficiently, often under mild conditions such as normal body temperature and pressure.
Enzymes do not get used up in the reaction. After the product is formed, it is released from the enzyme, and the enzyme is free to bind with another substrate molecule. The enzyme remains unchanged and can be reused multiple times.
Options a, b, and c are incorrect. Option a wrongly claims that products increase activation energy, but enzymes actually decrease it. Option b incorrectly describes products as substrates, which they are not. Option c falsely states that activation energy increases when the enzyme reacts with the substrate, but the opposite is true—the activation energy is decreased.
Therefore, the correct description of enzyme activity is that the substrate binds to the enzyme’s active site, enabling the enzyme to catalyze the reaction by lowering the activation energy and speeding up the process.