Lock and key mechanism

The active site of the enzyme is a cleft within the enzyme molecule which is complementary to the shape of the substrate ie. the substrate has an exact matching shape to the active site ^[1].

The shape of the active site of an enzyme means that the reaction that takes place will be very specific as only certain molecules are able to bind to it.

Once the substrate has bound to the active site of the enzyme, they form an enzyme substrate complex^[2][3].

Reference

1. ↑ Berg,J.M.,Tymoczko,J.L.,Stryer,L.(2007)Biochemistry, sixth ed, New York:W.H. Freeman and Company,pp.215
2. ↑ Lodish H., Berk A., Kaiser C., Krieger M., Bretscher A., Ploegh H., Amon A., Scott M., (2000) Molecular Cell Biology
3. ↑ Berg JM., Tymoczko JL., Gatto Jr GJ., Stryer L. (2015)Biochemistry, 8th Ed, New York: W.H. Freeman and Company. p224