Question

what is a induce-fit model?

Answer 1

starts with the active site open and substrate free in solution. The substrate approaches the enzyme and then binds at the active site.
Substrate binding causes a change in the shape of the enzyme such that the catalytic parts of the enzyme are brought to bear on the substrate. The chemical reaction occurs and the two products are left in the active site. For example, if sucrose is the substrate, the two products will be glucose and fructose. The two products leave the active site and the enzyme returns to its original active site open configuration.