Which of the following molecules binds to the active site of an enzyme?

• A. Coenzyme
• B. Inhibitor
• C. Allosteric regulator
• D. Substrate

Answer: (D)

Verified step by step guidance

1. Understand the role of an enzyme in a biochemical reaction: Enzymes are proteins that act as catalysts to speed up chemical reactions without being consumed in the process.
2. Identify the active site of an enzyme: The active site is a specific region on the enzyme where the substrate binds. It is typically a pocket or groove on the enzyme's surface.
3. Define what a substrate is: A substrate is the specific molecule upon which an enzyme acts. It binds to the enzyme's active site, forming an enzyme-substrate complex.
4. Differentiate between the molecules listed: Coenzymes are non-protein molecules that assist enzymes, often by carrying chemical groups between enzymes. Inhibitors are molecules that decrease enzyme activity by binding to the enzyme, either at the active site or elsewhere. Allosteric regulators bind to sites other than the active site, causing a change in enzyme activity.
5. Conclude that the substrate is the molecule that directly binds to the active site of an enzyme, initiating the catalytic process.