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Structural Organization of Proteins…read more

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Haemoglobin Molecules
· Haemoglobins ­ a group of proteins that have a quaternary
structure composed of four polypeptide chains.
· Each polypeptide is associated with a heme group ­ which contains
a ferrous (Fe2+) ion.
· Each Fe2+ ion can bind with a single oxygen molecule.
· Each hemoglobin molecule can carry up to four molecules of
oxygen.…read more

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The role of Haemoglobin
· Role of hemoglobin ­ Transport of Oxygen
· To be efficient at transporting oxygen, hemoglobin must:
~ readily associate with O2 at surface where gas exchange takes place
~ readily dissociate from O2 at those tissues requiring it.
How does hemoglobin achieve these two contradicting requirements?
· Remarkable property of hemoglobin ­ it changes its affinity for O2
under different conditions.
· It achieves this because its shape changes in the presence of certain
substances such as CO2.
· In the presence of CO2, the new shape of hemoglobin binds more
loosely to oxygen. As a result, hemoglobin releases its oxygen.…read more

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Why different hemoglobins?
Lets look at hemoglobins at each end of a range:
· Hemoglobins with a high affinity for O2 ­ take up oxygen more
easily but release it less readily.
· Hemoglobins with a low affinity for O2 ­ take up oxygen less easily
but release it more readily.
There is a correlation between the type of hemoglobin in an organism
and factors such as environment in which it lived or its metabolic rate.
· An organism living in an environment with little O2 requires a
hemoglobin that readily combines O2. Provided that the organism'
s metabolic rate is low, the fact that this hemoglobin does not
readily release its O2 will not be a problem.
· An organism with high metabolic rate needs to release oxygen
readily into tissues. Provided that there is plenty of O2 in the
organism's environment, it is more important to have a
hemoglobin that releases its O2 easily than one that takes it up
easily.…read more

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Why do different hemoglobins have different affinities for
O2?
· The answer lies in the shape of the molecule.
· Different hemoglobin molecules have slightly different amino acid
sequences & therefore slightly different shapes.
· Depending on the shape, hemoglobin molecules range from those
that have a high affinity for O2 to those that have a low affinity for
O2.
Loading & Unloading Oxygen
· The process by which hemoglobin combines with oxygen is called
Loading or associating. In humans this takes place in lungs.
· The process by which hemoglobin releases its oxygen is called
Unloading or dissociating. In humans this takes place in tissues.…read more

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