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Haemoglobin
4 x Haem group + 4 x Polypeptide chain
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The Bohr Effect
100%
% saturation
of
haemoglobin
partial pressure of O2 (mmHg)
Plateau:
Haemaglobin has a high affinity for O2so is
highly saturated even if there is not much O2
Makes the haemaglobin load up with O2 in
lung
Steep slope:
A small drop in the amount of O2means the haemaglobin
has a much lower affinity for O2
The haemaglobin is less saturated with oxygen as it gives itup to the tissues more easily.
This means the haemaglobin is highly effective in uptaking large amount of O2from the lungs but release it so easily to the tissue cells
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Bohr effect the effect of CO2 on haemoglobin
% saturation of
haemoglobin
partial pressure of O2 (mmHg)
Higher CO2 e.g. tissue cells
curve shift to the right
in actively respiring tissue cells, O2 is more easily released by haemoglobin !
haemoglobin has a lower
affinity to O2
Lower CO2 e.g. in lung curve shift to the left
haemoglobin has a higheraffinity to O2
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Oxygen dissociation curve: Haemoglobin VS Myoglobin
% saturation of
haemoglobin
partial pressure
of O2 (mmHg)
Haemoglobin
Myoglobin stores O2 in muscles and release it only whenthe O
2
partial pressure is very low.
Myoglobin
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Oxygen dissociation curve:
Foetal VS Maternal
% saturation of
haemoglobin
partial pressure
of O2 (mmHg)
Maternal
Foetal haemoglobin has higher affinity to O2 so as obtain
O2 from maternal blood in the placenta.
Foetal
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Transport of carbon dioxide
CO2 is carried by your blood in three ways:
5% carried in solution in the plasma as CO2
10% combines with the haemoglobin to form
carbamino-haemoglobin
85% is carried in red blood cells as hydrogen
carbonate: HCO3-
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Formation of hydrogen carbonate CO2diffuses from tissues into red blood cells.
The RBCs contain an enzyme called carbonic anhydrase
which catalyses the reaction between CO2and water toform carbonic acid:
CO2 + H2O H2CO3
Carbonic acid dissociates into negatively charged
hydrogen carbonate and positively charged hydrogen ions:H2CO3 H+ + HCO3
-
The hydrogen ions (H+) increase the acidity of the bloodand combine with Haemoglobin to give haemoglobinic acid.
This decreases the affinity of haemoglobin to oxygen soit gives it up to the tissues (the Bohr effect)
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Formation of hydrogen carbonate The build up of hydrogen carbonate ions causes
them to diffuse out of the RBC leaving the insideof the RBC positively charged.
In order to balance this electric charge, chlorideions diffuse into the RBCs from the plasma this isknown as the chloride shift.
At the lungs, all these reactions are reversed: The hydrogen carbonate and hydrogen ions
recombine releasing CO2.
The chloride shift is reversed. Carbamino-haemoglobin breaks down to release
CO2.
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