Anconeus Muscle - Attachments, Action & Innervation
Hemoglobin Molecule – Structure & Function
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Hemoglobin is a protein that binds with oxygen in the human bloodstream and delivers it to cells throughout the body. 
Inside each red blood cell are 200-300 million molecules of hemoglobin (Hb) molecules.
Hemoglobin is a large molecule composed of two alpha subunits and two beta subunits.
- Making up each subunit is a large, folded, polypeptide called globin. Between each two of the globin folds, there is a hydrophobic pocket that contains a heme group. Two histidine molecules are associated with each heme group.
Structure of Hmoglobin Subunits
- An expanded view of the Heme group reveals that it consists of an atom of ferrous iron (Fe2+) and a surrounding porphyrin ring (four nitrogen-containing pyrrole molecules). The iron atom can reversibly bind with one molecule of oxygen (O2).
Expanded view of the Hemoglobin molecule
- On one side of the heme group is the proximal histidine, which binds the Fe2+ of the Heme to the nearby globin. It helps stabilize the position of the attached Heme. The distal histidine, which is not bound to the heme, helps prevent oxidation of Fe2+ to Fe3+. Oxygen does not bind to Fe3+.
- Because it has four subunits, a hemoglobin molecule can reversibly bond with up to four O2 molecules. When not bonded to O2, deoxyhemoglobin stays in a tensed state (or conformation). The first O2 molecule to bond causes the oxyhemoglobin to shift to a
relaxed state. This change in shape makes it easier for additional O2 molecules to bind to the other Heme groups, a property called cooperativity.
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