Haemoglobin and the Bohr effect

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  • Created on: 11-05-14 15:49
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The carriage of oxygen
Oxygen is carried by the haemoglobin in erythrocytes. This makes the haemoglobin oxygenated
and makes it oxyhaemoglobin:
Oxygen + haemoglobin oxyhaemoglobin
Haemoglobin is a quaternary structure protein that has 4 tertiary structure polypeptide chains
and a haem (Fe2+) group at the centre of each. Each haem group has an affinity for oxygen and
can carry one molecule each (therefore each haemoglobin molecule can carry 4 oxygen
molecules)
This is a haemoglobin dissociation curve.
The pressure of oxygen in the air you breathe is called
`partial pressure of oxygen' or `oxygen tension'. As oxygen
tension rises, the likelihood oxygen will bind with
haemoglobin increases too.
A is the loading tension, which is usually when the
blood is near the lungs
B is the unloading tension, which is in respiring cell
and tissues.
The loading tension of fetal haemoglobin is at the same
point as the unloading tension of adult haemoglobin. Fetal haemoglobin also has a higher affinity
with oxygen than adults, both of which are critical during pregnancies.
The carriage of carbon dioxide
Carbon dioxide can be carried in 3 different ways:
Dissolved in blood plasma
It combines with haemoglobin to form carbaminohaemoglobin
Most of it is converted to hydrogencarbonate ions (HCO3)
How are hydrogencarbonate ions formed?
Carbon dioxide enters erythrocytes, and combines with water to form carbonic acid. The
enzyme carbonic anhydrase catalyses this reaction...
CO2 +H2O H2CO3
The carbonic acid dissociates into hydrogencarbonate ions and hydrogen ions...
H2CO3 HCO3 + H+
The hydrogencarbonate ion then diffuse out of the erythrocytes into the plasma. At the same
time, chlorine ions diffuse into the cells to balance the charge of the cell, this is called chloride
shift.

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As acid are H+ donors, and there are lots of H+ ions in the erythrocytes, the haemoglobin bonds
with them to form haemoglobinic acid. It is acting as a buffer (maintaining the pH level).
The Bohr effect:
The H+ ions from the dissociation of carbonic acid compete with oxygen molecules to bond with
the haemoglobin, therefore the oxyhaemoglobin will release more oxygen.…read more

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