In biochemistry, which statement best defines an enzyme?

• A. A non-specific solvent that accelerates all reactions equally by increasing temperature
• B. A molecule that increases reaction rate by raising the activation energy to favor product formation
• C. A biological catalyst, usually a protein (or sometimes RNA), that increases the rate of a specific chemical reaction by lowering the activation energy without being consumed
• D. A reactant that is permanently used up during a reaction and must be replenished after each catalytic cycle

Answer: (C)

Verified step by step guidance

1. Understand that enzymes are biological molecules that act as catalysts in biochemical reactions.
2. Recall that a catalyst increases the rate of a reaction by lowering the activation energy, not by raising it.
3. Recognize that enzymes are usually proteins, although some RNA molecules (ribozymes) can also act as enzymes.
4. Note that enzymes are specific to particular reactions and are not consumed or permanently altered during the reaction, meaning they can be reused.
5. Eliminate options that describe enzymes as non-specific solvents, reactants, or molecules that increase activation energy, and identify the correct definition as a biological catalyst that lowers activation energy to speed up specific reactions.