Which of the following is an example of a biological catalyst?

• A. Nucleotides
• B. Lipids
• C. Enzymes
• D. Sugars

Answer: (C)

Biological catalysts speed up chemical reactions in living organisms by lowering the activation energy needed for those reactions to proceed. The classic example of a biological catalyst is an enzyme, usually a protein with an active site shaped to fit a specific substrate. When the substrate binds, the enzyme helps orient and stabilizes the transition state, making the reaction occur faster. Enzymes are not consumed in the process and can be reused, which is why they’re such efficient facilitators of biochemical steps.

Nucleotides, lipids, and sugars each play essential roles in cells—nucleotides as the building blocks of nucleic acids (and carriers of energy like ATP), lipids in membranes and energy storage, and sugars as energy sources and structural components. However, they don’t act as catalysts that accelerate a wide range of reactions the way enzymes do.