Enzymes work by creating a location for molecules to bind together or break apart called the active site. When a molecule enters the active site, a chemical reaction takes place. The speed at which the chemical reaction occurs is determined by the action of the enzyme. Different enzymes are located in different areas of the body, with each enzyme working on only one type of molecule.
Enzyme function is controlled by inhibitors and activators. Inhibitors make the enzyme slow down or stop the reaction. They change the shape of the enzyme so that it either doesn't accept a molecule, or so that it accepts it more slowly. Activators are the opposite of inhibitors. They speed up the activity of enzymes. Hormones are often used to activate enzymes.
Enzymes can be altered by temperature and by the acidity of the environment. Each enzyme functions best within an optimal temperature range. Temperatures that are outside of this range may change the shape of the enzyme so that it is no longer usable. Each enzyme also operates within an ideal level of acidity, called a pH level. If an enzyme is placed in an environment with the wrong pH level the enzyme shape changes, and it is no longer able to function.