In a typical diagram of an enzyme-substrate complex, which labeled region represents the active site?

• A. C. The entire enzyme structure
• B. A. The pocket or groove on the enzyme where the substrate binds
• C. D. The product released after the reaction
• D. B. The substrate molecule itself

Answer: (B)

Verified step by step guidance

1. Understand the concept of an enzyme-substrate complex: Enzymes are biological catalysts that speed up chemical reactions by lowering the activation energy. The active site is the specific region on the enzyme where the substrate binds and the reaction occurs.
2. Visualize the structure of an enzyme: Enzymes are typically globular proteins with a unique three-dimensional shape. Within this structure, there is a pocket or groove that is specifically shaped to fit the substrate molecule. This is the active site.
3. Clarify the role of the active site: The active site is where the substrate binds through interactions such as hydrogen bonding, ionic interactions, or hydrophobic effects. This binding forms the enzyme-substrate complex, which facilitates the chemical reaction.
4. Differentiate the labeled regions: Option A refers to the pocket or groove on the enzyme where the substrate binds, which is the active site. Option B refers to the substrate molecule itself, which is not the active site. Option C refers to the entire enzyme structure, which includes regions beyond the active site. Option D refers to the product released after the reaction, which is not part of the active site.
5. Conclude that the active site is the pocket or groove on the enzyme where the substrate binds, as described in Option A. This region is critical for the enzyme's function and specificity.