The three-dimensional shape of an enzyme is important to its functioning. Enzymes have an active site which can 'recognize' and form a temporary association with specific substrate molecules. Enzymes are highly substrate specific. Each enzyme can only recognize and bind to one substrate, or to one group of closely related molecules. Because this substrate recognition depends on shape matching between the enzyme and its substrate, any change in the shape of the enzyme will interfere with its ability to bind substrate and catalyze reactions.
Enzymes are unchanged by the reactions that they catalyze.
An enzyme molecule can be used over and over again. A small amount of enzyme, given sufficient time, can catalyze many repeated reactions, eventually converting a large amount of substrate molecules to product. The binding site for the substrate is called the active site. Enzymes may have other binding sites, called control sites, which interact with other molecules. These other molecules may improve or interfere with the enzyme's ability to recognize and bind its substrate.