Oxygen Transport and Hemoglobin

Oxygen Transport

In mammals, oxygen is transported from the lungs throughout the body by red blood cells.  Red blood cells, referred to as erythrocytes, contain the respiratory pigment hemoglobin. Oxygen reversibly binds to hemoglobin to form oxyhemoglobin (HbO2).  The binding of oxygen to hemoglobin removes oxygen from solution and consequently allows more oxygen to be transported to the tissues.  Oxyhemoglobin then travels in the blood to body tissues.  When the oxyhemoglobin encounters deoxygenated tissues the oxygen dissociates from the hemoglobin to supply oxygen (Schmidt-Nielsen, 1997).  

A representation of the transport of oxygen to the tissues.  The equation for oxygen transport may be expressed as:  Hb + 4O2 = HbO2.   Image courtesy of Professor Robert J. Huskey at the University of Virginia.

Hemoglobin Structure and Properties 

Hemoglobin, the integral molecule for oxygen transport in erythrocytes, is found in nearly all mammals.  Hemoglobin is composed of the protein Globulin, which consists of four polypeptide (gray) chains and four nitrogen-containing (blue) cyclic organic molecules called hemes (Ball and Stick).  The protein of hemoglobin is composed of two identical polypeptide alpha chains and two identical polypeptide beta chains (Bouverot, 1985).  Each of the four polypeptide chains binds to a heme group that is then bonded to a central iron ion (gold).  Each iron is capable of binding one oxygen atom, thus hemoglobin binds a total of four oxygen atoms (Ball and Stick).

Hemoglobin is capable of binding and releasing oxygen by changing conformations which attract or repel molecules of oxygen.  Hemoglobin is in a "tense" state, commonly called the T state, when oxygen is bound.  In the absence of oxygen, hemoglobin conforms to a "relaxed" state, the R state.  The T  state is characterized by a high affinity for oxygen whereas the R state has a very low affinity for oxygen (T and R State).  



Images used with cooperation of Carol Stone.

Main Page     The Oxygen Dissociation Curve     Hypoxia     Llama      Deer Mice     Conclusion      Acknowledgements     

Literature Cited     

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Last Updated November 28, 1999

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