This document discusses enzymes and coenzymes. It defines enzymes as proteins that catalyze biochemical reactions and notes they have molecular weights ranging from 10,000 to 200,000. Coenzymes are organic non-protein molecules that bind to apoenzymes to form active enzymes. There are two types of enzymes - exoenzymes act outside cells while endoenzymes act inside cells. The International Union of Biochemistry classifies enzymes into six major classes based on the type of reaction catalyzed, including oxidoreductases, transferases, hydrolases, lyases, and isomerases. Enzymes exhibit a high degree of specificity in their catalytic actions and function via the Michaelis-