So this is what the hemoglobin, the hemoglobin protein, actually looks like. We have subunit one shown in green, subunit two shown in purple, subunit three shown in brown and subunit four shown in orange. Now, notice that within each one of these subunits, we have a hydrophobic section right inside. So these red sections basically are the heme groups. They're a percent of groups that are found within each subunit and each one of these heme groups, so we have 1234. Each one of these contains a single iron atom.