Enzymes contain a(n) that is formed to fit a specific type of . Once the binds to the enzyme, a reaction takes place and are formed. Enzymes function by the activation energy required for the reaction to take place. Enzymes are regulated by conditions that change the shape of their , meaning that they function best at a specific temperature and pH. For example, within the digestive system, is an enzyme that functions in the stomach, which has a pH of 2.0. In contrast is an enzyme that functions in the small intestine, which has a pH of 7.35. By changing the pH between the stomach and small intestine, it is possible to turn off and turn on.

Enzymes contain a(n) active site that is formed to fit a specific type of substrate . Once the substrate binds to the enzyme, a reaction takes place and products are formed. Enzymes function by decreasing the activation energy required for the reaction to take place. Enzymes are regulated by conditions that change the shape of their active site , meaning that they function best at a specific temperature and pH. For example, within the digestive system, pepsin is an enzyme that functions in the stomach, which has a pH of 2.0. In contrast trypsin is an enzyme that functions in the small intestine, which has a pH of 7.35. By changing the pH between the stomach and small intestine, it is possible to turn trypsin off and turn pepsin on.