Now, what the active side does, what enzymes actually do is they bring the substrate molecules into this very small region of space that creates a microenvironment for that reaction. So inside the active side, we create a microenvironment that not only brings those substrate molecules in close proximity, but it also orients those substrate molecules in the proper orientation so that reaction can actually take place. For instance, if we go back to Covalent catalysis. Another reason why covalent contalisis might take place is because once we attach this group onto the active side, that orients that group in just the proper orientation for the next step in the reaction to actually take place. So many biological reactions involve two or more substrate molecules. And this implies that for a reaction to actually take place, they must be close enough and must also have the proper orientation.