Please be descriptive and use examples. Also provide reference of where you got the information so I may use in the future. The role of catalysts is critical in many chemical reactions. They have great consequence in the fields of medicine and pharmacology.

Identify the two important classes of catalysts.

Choose a catalyst that exists in the human body. Explain its importance and how it works.
Analyze the chemical reactions that take place when a biological catalyst combines with a reactant (substrate) to form an unstable intermediate.