And this molecule, the two three BPG, contains 12345 negative charges. And that's exactly why this molecule is able to bind at the center pocket, because there is a strong electric attraction between these negative charges and the positive charges found along the following six amino acids. So this is the two three BPG molecule, and it binds the electrostatic forces with these six amino acids. Now, this is normal hemoglobin that is found in our bodies. But when the fetus is developing inside the mother, the gene that expresses the hemoglobin expresses a slightly different hemoglobin. So the fetal hemoglobin molecule also contains the alpha one and the alpha two subunits, but it does not contain beta one and beta two.