Enzymes are biological catalysts.
Catalysts increase the rate of chemical reactions.
A catalyst is not altered by the reaction. A catalyst does not change the final result of a reaction. The activation energy is the amount of energy needed by the reactant molecules to participate in a reaction. In the absence of a catalyst, only a small proportion of the reactants possess the activation energy to participate in the reaction. By lowering the activation energy, enzymes allow a larger proportion of the reactants to participate in the reaction, thus increasing the reaction rate.