What is an enzyme?

• A. A protein made up of amino acids acts as a biological catalyst.
• B. A lipid used for energy storage.
• C. A carbohydrate that provides quick energy.
• D. A nucleic acid that stores genetic information.

Answer: (A)

An enzyme is a biological catalyst that speeds up chemical reactions in living organisms by lowering the activation energy needed to start the reaction. Most enzymes are proteins made of amino acids that fold into a specific three-dimensional shape, creating an active site where the substrate binds with high specificity. This specificity means each enzyme typically acts on a particular substrate or type of chemical reaction. Enzymes can be reused and are sensitive to conditions like temperature and pH; extreme conditions can denature them and reduce activity. The other options describe molecules with different roles—lipids store energy, carbohydrates provide quick energy, and nucleic acids store genetic information—so they don’t fit the function of enzymes.