Which one of the following statements holds true for the induced-fit model? a) once the enzyme binds to the specific substrate molecule , no structural changes can occur in the active site in the enzyme . b) once the enzyme binds to the specific substrate molecule , structural changes can occur in the active site to accommodate the product . c) once the enzyme binds to a specific substrate molecule , subtle structural changes can occur in the active site , which are reverted when the reaction is over .