What is an active site of an enzyme?

The active site of an enzyme refers to the specific region of an enzyme where a substrate binds to and catalyzes a chemical reaction. The active site is a structural element of protein. It is formed by the folding pattern of the protein and appears as a pocket or groove that is shaped to accommodate the structure of the enzyme that works on it. Only this region of the enzyme is capable of binding to the substrate. Generally, every enzyme has only one active site that fits with only one specific substrate. Residues that occur at the active site, form temporary hydrogen bonds with the substrate at the binding site to form an enzyme-substrate complex.