) What is the definition of an enzyme? A. Enzymes are carbohydrate molecules that act as catalysts to speed up chemical reactions in living things. B. Enzymes are polymer molecules that act as catalysts to slow down chemical reactions in living things. C. Enzymes are protein molecules that act as catalysts to speed up chemical reactions in living things. D. Enzymes are fat molecules that act as catalysts to speed up chemical reactions in living things. E. Enzymes are protein molecules that act as catalysts to slow down chemical reactions in living things.