In enzyme catalysis, can a single enzyme molecule be used more than once to catalyze repeated reactions?

• A. Yes, but only if the reaction has a negative Gibbs free energy change ($\Delta G<0$).
• B. No; the enzyme is irreversibly converted into product during the first catalytic cycle.
• C. Yes; the enzyme is not consumed in the reaction and can catalyze multiple substrate molecules.
• D. No; each enzyme molecule can catalyze only one reaction before it must be resynthesized by the cell.

Answer: (C)

Verified step by step guidance

1. Understand the role of enzymes in biochemical reactions: enzymes act as catalysts that speed up reactions without being consumed or permanently altered in the process.
2. Recall that enzymes lower the activation energy of a reaction but do not change the overall Gibbs free energy change (\$\(\Delta\) G\$) of the reaction.
3. Recognize that because enzymes are not consumed or changed irreversibly, a single enzyme molecule can catalyze multiple substrate molecules repeatedly.
4. Note that the direction or spontaneity of the reaction (whether \$\(\Delta\) G < 0\$ or not) does not affect the enzyme's ability to be reused; it only affects whether the reaction proceeds spontaneously.
5. Conclude that the correct understanding is: enzymes are reusable catalysts and are not consumed during the reaction, allowing them to catalyze many cycles.