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What is it?
Haemoglobin is a protein with several important properties:
it occurs in red blood cells, where it has a vital role in oxygen transport
it is a protein with a quaternary structure because it is made from four polypeptide
it has the remarkable ability to pick up oxygen where it is abundant (the lungs) and
release it where it is needed (the respiring tissues)
The role of haemoglobin in the transport of oxygen
Oxygen is carried mainly as oxyhaemoglobin in the red blood cells.
A key point about haemoglobin is not that it can
pick up oxygen, lots of substances can do that, but
that it can releaseit again in areas where is it
needed. The behaviour of oxygen is illustrated by
the oxygen dissaciation curve.
Region of Oxygen Carbon dioxide Affinity of Result
Body concentration concentration haemoglobin
Gas exchange High Low High Oxygen is
surface (lungs) attached
Respiring Low High Low Oxygen is
Loading, transport and unloading of oxygen
at the gas-exchange surce carbon dioxide is constantly being removed
the pH is raised due to the low level of carbon dioxide
the higher pH changes the shape of haemoglobin into one that enabes it to load
the shape also increase the affinity of haemoglobin for oxygen, so it is not released
while being transported by the blood to the tissues
in tissues carbon dioxide is produced by respiring cells
carbon dioxide is an acidic solution, so the pH of the blood within the tissues is
the lower pH changes the shape of haemoglobin into one with a lower affinity for
haemoglobin releases its oxygen into the respiring tissues.
Why are there different Haemoglobins?
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Haemoglobins have different affinities for oxygen. High affinity means it takes up
oxygen easily but releases it less readily, low affinity means it takes up oxygen less easily
but releases it readily.
An organism living in an enviroment with little oxygen requires a haemoglobin that readily
combines with oxygen if it is to absorb enough of it. provided that the metabolic rate s not
very high, that fact it does not release oxygen as readily is not a problem.…read more