Oxygen and carbon dioxide are carried in the blood, pumped by the heart, and shifted through membranes by partial pressure gradients. Oxygen dissolves to a much smaller degree than carbon dioxide, so that at rest, the PO2 would only help provide 6% of the body’s O2 requirements. There must be another way. The hemoglobin molecule comes to the rescue.
Hemoglobin is made of globin, a protein, and four heme groups consisting of an iron atom surrounded by an organic group. Four polypeptide chains make up the globin, each bearing a red-pigmented, disk-shaped heme. Each heme group binds one oxygen molecule, so each hemoglobin molecule binds four oxygens. Considering one red blood cell holds ~ 250 million Hb molecules, it can carry ~ 1 BILLION oxygen molecules (Marieb 581). The entire molecule… continue reading