And at the center of the heme group is the protiporphine ring. So the protoporphine ring basically is that organic part of that heme group that actually carries, that holds that iron atom. Now, in the process of the synthesis of this protoporphine ring, of the hemegroup, the final step is to basically use a special enzyme known as ferrokeletase to basically catalyze the insertion of that se atom, the metal atom, into the center of the protiporphine ring. Now, normally, the protoporphine ring has a planar shape, so the shape of it is relatively planar. But to actually fit that fe atom, the metal atom, into the center of that protoporphine, what this enzyme does, what the ferrocalitase does is it basically bends the shape of that protoporphine ring and then that exposes the electrons, the lone pair of electrons that can now bind that fe atom. And so what the ferrocalitase does is it basically catalyzes the bending of that planar shape of the protoporphrine molecule.