What is the part of an enzyme into which a substrate fits?

• A. Active site
• B. Cofactor
• C. Substrate binding pocket
• D. Allosteric site

Answer: (A)

Enzymes have a specific region where the substrate fits called the active site. The active site is shaped and lined with amino acids that interact with the substrate, bringing it into the correct orientation for the chemical reaction to occur. This selective fit explains why enzymes catalyze only particular reactions. A cofactor is a non-protein helper that can assist the enzyme’s function but isn’t the binding site for the substrate. The idea of a substrate binding pocket describes the groove that holds the substrate, but the standard term for the binding region is the active site. An allosteric site is a separate region where regulatory molecules bind to change the enzyme’s activity, not where the substrate binds. So, the part of an enzyme into which a substrate fits is the active site.