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AQA AS BIOLOGY UNIT 2
Primary Structure 4 polypeptide chains.
Secondary Structure Each of the polypeptide chains is coiled into a helix.
Tertiary Structure Each polypeptide chain is folded into a precise shape.
Quaternary Structure All 4 polypeptide are linked to form a spherical molecule. Each polypeptide is
associated with a haem group which contains an iron ion (combines with a single O2 molecule making 4 O2
molecules carried by a single haemoglobin molecule).
The Role of Haemoglobin
Haemoglobin's role is to transport oxygen efficiently.
For the efficient transportation of oxygen to occur, haemoglobin must;
Readily associate with oxygen at the surface where gas exchange
Readily dissociate from oxygen at tissues requiring O2.
When carbon dioxide is present, the shape of haemoglobin changes slightly. This change means that oxygen binds
more loosely so the oxygen is released.
Why Have Different Haemoglobins?
Haemoglobins with a high affinity for oxygen take up oxygen more easily but release it less readily.
Haemoglobins with a low affinity for oxygen take up oxygen less easily but release it more readily.
An organism in an environment with little oxygen requires haemoglobin that readily combines with oxygen.
An organism with a high metabolic rate needs to release oxygen readily into its tissues.