Catalysts play an important part in many chemical processes. A catalyst is a substance that speeds up the rate of a chemical reaction by lowering its activation energy. A catalyst does not get permanently changed and does not get used up in the reaction. Catalysts are important in many industrial chemical applications, as well as in biochemical reactions. In biological systems, the most common catalysts are protein molecules, called enzymes. Enzymes act as catalysts in virtually all chemical reactions within cells.