Enzymes are protein molecules that have a three dimensional globular shape. Their function is to speed up the rate at which chemical reactions take place, particularly within the cells of organisms. Enzymes are therefore referred to as biological catalysts. These events take place in the distinct groove or “active site” of the enzyme molecule and involve the binding of the reaction chemical or “substrate”, and the breaking or making of chemical bonds. The outcome is a specific change to the substrate, which creates a new chemical molecule or “product”. The enzyme molecule itself is unchanged by the event. Enzymes are classified into six groups according to the type of chemical reaction they catalyse (