Enzymes as catalysts

Enzymes are catalysts which raise the rate of a chemical reaction without being modification themselves in the procedure.  In the absence of an enzyme the reaction may difficultly proceed at all, while in its presence the rate can be increased up to 107-fold. Enzyme catalyzed reactions commonly take place under relatively mild conditions  temperatures  well  below  100^.C, atmospheric  pressure  and  neutral pH as compared  with the corresponding  chemical  reactions. The Enzymes are also highly specific with respect to the substrates on that they act and the products in which they form.  Additionally,   enzyme   activity can be regulated varying   in response to the concentration of substrates or other molecules.  Nearly all enzymes are proteins, while a few catalytically active RNA molecules have been recognized.