Which statement best describes an enzyme?

• A. An enzyme is a structural carbohydrate found in plant cell walls.
• B. An enzyme is a nucleic acid that carries genetic information.
• C. An enzyme is a type of lipid that stores energy in cells.
• D. An enzyme is a biological catalyst that speeds up chemical reactions without being consumed.

Answer: (D)

Verified step by step guidance

1. Step 1: Begin by understanding the definition of an enzyme. An enzyme is a protein (or sometimes RNA) that acts as a biological catalyst, meaning it speeds up chemical reactions without being consumed in the process.
2. Step 2: Eliminate incorrect options by analyzing their descriptions. For example, structural carbohydrates like cellulose are found in plant cell walls, but they are not enzymes.
3. Step 3: Recognize that nucleic acids, such as DNA and RNA, carry genetic information, but they are not enzymes unless referring to catalytic RNA (ribozymes).
4. Step 4: Understand that lipids, such as triglycerides, store energy in cells, but they are not enzymes.
5. Step 5: Conclude that the correct description of an enzyme is 'a biological catalyst that speeds up chemical reactions without being consumed.' This aligns with the fundamental role of enzymes in biochemistry.