Enzymes are proteins, composed of polypeptide chains and non-protein groups. Their function is to help with the reactions of many cells and molecules by serving as catalysts. A catalyst is a substance that allows the activation energy required for a reaction by forming a temporary association with the molecules that are reacting. During this process, the catalyst itself is not permanently altered in the process, and so it can be used over and over again. Because of catalysts, cells are able to carry out chemical reactions at a great speed and at comparative low temperatures. Almost 2,000 different enzymes are now known, each of them capable of cat