HAEMOGLOBIN

                                         HAEMOGLOBIN                                                         –                                                                                                                          Body cells need a constant supply of oxygen.Oxygen  is transported around the body inside red blood cells.Each haemoglobin molecule is made up of four polypeptides.                                                    Each haem group combine with one oxygen molecule                                                                       –      Hb +4O2  =   HbO8                                                                                                                 Haemoglobin molecules that transport oxygen :                                                                           1.Pick up oxygen at the lungs                                                                                                  2.Release oxygen within respiring tissues                                                                         3.Investigating how Haemoglobin behaves.
       Investing how haemoglobin behaves:

•  ž  Extract samples from blood
•  ž  Expose samples to different partial pressures
• ž      Measure amount of oxygen which combines with each sample of haemoglobin   NOTE:Maximum amount of oxygen that haemoglobin sample can combine with is 100% and therefore said to be saturated .Saturation of haemoglobin with oxygen is therefore measured in percentage and can be plotted against partial pressure of oxygen to obtain a curve.                                                                      

ž  Haemoglobin from lungs carries a lot of oxygen as it reaches a muscle ,it releases around ¾ of oxygen which diffuses out of red blood cell and into muscle where it can be used in respiration.

ž  S –shaped curve.

ž  Shape of dissociation curve can be explained by behaviour of haemoglobin molecule                                                                                                                                                                                 

ž  When an oxygen molecule combine with one haem group , the whole haemoglobin is slightly distorted.                                                                                                                                                                                                

  Bohr   Shift:

      Behaviour of haemoglobin in picking up oxygen at the lungs and readily releasing it when in low  in oxygen partial pressure                                                                                                

ž  Amount of oxygen,the haemoglobin carries is also affected by the partial pressure of carbon dioxide.

ž  It diffuses from cells and into blood plasma and some diffuses into red blood cells.

ž  In cytoplasm of RBCs there is an enzyme carbonic anhydrase that catalyze the reaction:

ž  CO2 + H2O =H2CO3 (carbonic acid )                  [  DISSOLUTION ]

ž  Hydro carbonic acid dissociates=H2CO3 oxygen ion  + Hydrogen carbonate ion             [DISSOCIATION]

ž  Haemoglobin combines with hydrogen ions forming haemoglobinic acid ,HHb. Result of this reaction is in two – fold:

• ž. Haemoglobin ‘mops up’ the hydrogen ions which are formed when CO2 dissolves and dissociates.
• ž       Presence of high partial pressure of carbon dioxide causes haemoglobin to release oxygen.

               Carbon Dioxide Transport

ž  Bohr effect explains one way in which CO2 is carried in the blood .Another product of dissociation of dissolved carbon dioxide is hydrogen carbonate ions.

ž  Hydrogen carbonate ions is formed in cytoplasm of RBCs because of presence of enzyme carbonic anhydrase .

ž  Some CO2 molecules does not dissociate but remain as CO2 molecules and dissovle in blood plasma.

ž  Other CO2 molecules diffuse into RBCs and combine directly with terminal amine groups (-NH2) of some haemoglobin molecules.