Enzymes are some of the vital "cogs" of our body. They are macromolecular biological catalysts that accelerate chemical reactions. The molecules affecting enzymes directly are called substrates, and then the enzyme transforms the substrates into various molecules known as products. Coenzymes are small organic molecules that bind tightly or loosely to the enzyme. By binding to the enzyme's active "site," it helps the enzyme do the job of making or breaking down substrates into products.