Now, why would we want to form a Covalent bond? Well, one reason is to basically keep that substrate molecule in place inside the active side. So many enzymes contain active sites with catalytic residues that can form temporary Covalent bonds with the substrate molecule and that can be used to basically keep that molecule in place for the time being until that reaction actually takes place. Now, at the end of the reaction, because we always have to regenerate our enzyme, the enzyme is never used or depleted or changed in any reaction. We have to break that bond. And that's exactly why we call this bond a temporary or a transient Covalent bond.