Enzymatic reactions can be broadly classified into six categories: 1. Oxidoreductases - Involved in oxidation-reduction reactions. 2. Transferases - Transfer functional groups between molecules. 3. Hydrolases - Catalyze the hydrolysis of various bonds. 4. Lyases - Break bonds by means other than hydrolysis and oxidation. 5. Isomerases - Facilitate the rearrangement of atoms within a molecule. 6. Ligases - Join two molecules together with covalent bonds.