Many enzymes function by lowering the activation energy of reactions. By bringing the reactants closer together, chemical bonds may be weakened and reactions will proceed faster than without the catalyst. Image from W.H. Freeman and Sinauer Associates, used by permission. Carbonic anhydrase speeds up the transfer of carbon dioxide from cells to the blood. There are over 2000 known enzymes, each of which is involved with one specific chemical reaction.
Enzymes are substrate specific.
Enzymes are proteins. The functioning of the enzyme is determined by the shape of the protein. It recognizes, confines and orients the substrate in a particular direction. Space filling model of an enzyme working on glucose. Image from W.H. Freeman and Sinauer Associates, used by permission.