Hemoglobin

Hemoglobin is the protein in blood that is rich in iron and gives it the red color. It makes up about 95% of a red blood cell and has an oxygen binding capacity of 1.34 mL O2/g, which satisfies the need for the average adult consumption of 250 mL of oxygen per minute. Hemoglobin is a globular protein structured as two α and two β helices. The amino acid histidine is hydrogen bonded to one of the NH group residues or the O in the CO group. Four heme groups carry the iron in hemoglobin. Each group contains one iron atom, which binds to the nitrogen molecule of the histidine residue on one end of the group and to one oxygen molecule, allowing one hemoglobin protein to bind to four oxygen molecules. Iron-rich hemoglobin flows through the bloodstream, returning to the lungs where oxygen is taken in during inhalation. The oxygen is picked up by the hemoglobin and binds to the iron, and the hemoglobin becomes oxyhemoglobin. The Bohr effect describes the exchange cycle in which blood returns to the body to distribute the O2 molecules and picks up the CO2 from the capillaries, whereby oxyhemoglobin becomes deoxyhemoglobin.