Which term describes a specific reactant that is acted upon by an enzyme?

• A. Cofactor
• B. Inhibitor
• C. Product
• D. Substrate

Answer: (D)

Verified step by step guidance

1. Understand the role of enzymes in biochemical reactions: Enzymes are biological catalysts that speed up chemical reactions by lowering the activation energy required for the reaction to occur.
2. Learn the definition of a substrate: A substrate is the specific reactant molecule that an enzyme binds to and acts upon during a biochemical reaction.
3. Differentiate between the given terms: Cofactor refers to a non-protein molecule or ion that assists enzyme activity, inhibitor refers to a molecule that decreases enzyme activity, and product refers to the molecule(s) formed after the reaction. Substrate is the correct term for the reactant acted upon by the enzyme.
4. Visualize the enzyme-substrate interaction: The substrate binds to the enzyme's active site, forming an enzyme-substrate complex. This interaction is highly specific, often described as a 'lock and key' model.
5. Conclude that the correct term for the specific reactant acted upon by an enzyme is 'substrate,' based on the definitions and roles of the terms provided.