The organic molecules that catalyze reactions in living systems are called enzymes. Enzymes are proteins that act as catalysts, which means they speed up the rate of a chemical reaction without being consumed in the reaction. Enzymes are highly specific, each one catalyzing a particular reaction or set of reactions. They do this by providing a favorable environment for the reaction to occur, lowering the activation energy and increasing the rate of the reaction. Enzymes are essential for the proper functioning of all living organisms, and without them, many of the essential chemical reactions in the body would not occur at a fast enough rate to sustain life.