Enzymes are mainly made up of proteins that undergo complex coiling and folding to form tertiary structure, due to this coiling and folding 3 - 13 reactive amino acids comes close together forming a cavity or cleft known as an active site. The specific substrate binds to active site forming ES complex, which is an unstable transient stage forming product and the enzyme remains unchanged. Generally, the enzymes are having one active site specific to the substrate.