When there are two or more reactants, the active site provides a template on which the substrates can come together in the proper orientation for a reaction to occur between them 2.as the active site of an enzyme clutches the bound substrates, the enzyme may stretch the substrate molecules toward their transition state form, stressing and bending critical chemical bonds to be broken during the reaction. because ea is proportional to the difficulty of breaking the bonds, distorting the substrate it approach the transition state and reduces the amount of free energy that must be absorbed to achieve that state. 3.the active site may also provide a microenvironment that is more conducive to a particular type of reaction than the solution itself would be without the enzyme. ex: if the active site has amino acids with acidic r-groups, the active site may be a pocket of low ph in an otherwise neutral cell. in such cases, an acidic amino acids may facilitate h+ transfer to the substrate as a key step in catalyzing the reaction. 4. amino acids in the active site directly participate in the chemical reaction. sometimes this process even involves brief covalent bonding between the substrate and the side chain of an amino acid in an enzyme. subsequent steps of the reaction restore the side chains to their original states so that the active site is the same after the reaction was before?