Final answer:
Enzymes are used repeatedly in biochemical reactions, catalyze only specific types of reactions, are not consumed by the reaction, and do not change the free energy change of the reactions they facilitate.
Step-by-step explanation:
The characteristic of enzymes that is most relevant to the student's question is that they are used over and over again. This property is essential to their biological roles as catalysts. Enzymes facilitate the chemical reactions necessary for life by reducing the activation energy required for reactions to occur, yet they themselves are not consumed by these reactions. After catalysis, enzymes release their product(s) and are free to catalyze new reactions. One significant aspect of enzyme function is their specificity; they tend to be highly specialized for certain reactions and typically catalyze only a few related types of reactions. In addition, enzymes do not affect the overall free energy change (ΔG) of the reactions they catalyze, meaning they cannot change an endergonic reaction (one that requires energy input) into an exergonic one (one that releases energy).