So remember, the heme group shown here consists of the organic component that is known as the protoporphrine. And it also contains that inorganic metal atom, that iron atom. Now, the iron atom is attached to the proximal HistoGene amino acid that is attached to this polypeptide chain. And notice that because the oxygen is not attached to our iron atom, that iron atom is found below the plane of that protoporphine. Because when it's not balanced as an oxygen, the iron is simply too large of an atom. It contains a large electron density.