As an enzyme fits into a substrate at the active site it undergoes a slight change to fit into the substrate. This process is denied by a concept known as the Induced Fit Model. The concept believes that the active site and the substrate are a fit for each other just like puzzle pieces that fit together. That is how when an enzyme finds its fit, that is when the chemical reaction can begin. After the reaction is complete, the enzymes detaches itself and finds another active site.
