What is the role and structure of enzymes in the human body?

The role of enzymes are to act as a catalyst to speed up the rate of chemical reactions within the human body. They do this by binding to a molecule or substrate and breaking it up or by combining two molecules together. Enzymes are proteins that have been molded in such a way to create a binding site that substrate molecules can attach to. Enzymes have different shapes and each enzyme is specific to its substrate molecule in such a way that only its selected substrate can fit into its binding site. This is known as the lock and key hypothesis.