Which of the following correctly completes the sentence: "The ______ binds to the ______ site on an enzyme."?

• A. cofactor; regulatory
• B. substrate; active
• C. enzyme; allosteric
• D. product; catalytic

Answer: (B)

Verified step by step guidance

1. Understand the structure and function of an enzyme: Enzymes are biological catalysts that speed up chemical reactions. They have specific regions called active sites where substrates bind and undergo a chemical reaction.
2. Define the key terms: The 'substrate' is the molecule upon which an enzyme acts. The 'active site' is the specific region on the enzyme where the substrate binds and the reaction occurs.
3. Analyze the sentence structure: The sentence is describing a relationship between two components of an enzymatic reaction. The blank spaces need to be filled with terms that correctly describe this interaction.
4. Evaluate the options: (1) Cofactor; regulatory - Cofactors are non-protein molecules that assist enzymes but do not bind to the active site. (2) Substrate; active - This is correct because the substrate binds to the active site. (3) Enzyme; allosteric - Enzymes can have allosteric sites, but this does not fit the sentence structure. (4) Product; catalytic - Products are the result of the reaction and do not bind to the catalytic site.
5. Conclude that the correct completion of the sentence is: 'The substrate binds to the active site on an enzyme.' This aligns with the fundamental principles of enzyme-substrate interactions.