Transport of oxygen by haemoglobin
- Created by: Kittykatty2000
- Created on: 19-04-17 18:10
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Oxygen dissociation curves:
The graph of the relationship between the saturation of haemoglobin with oxygen and the partial pressure of oxygen
1.
- Shape of the haemoglobin molecule makes it difficult for the first oxygen molecule to bind to one of the sites on its four polypeptide chains because they are closely united
- Therefore at low concentration gradients, little oxygen binds to the haemoglobin
- The gradient of the curve is shallow initially
2.
- Howver, the binding of the first oxygen molcule changes the quaternary structure of the haemoglobin molecule, causing it to change shape
- This change makes it easier for the other subunits to bind to an oxygen molecule
3.
- It therefore takes a smaller increase in the partial pressure of oxygen to bind the second oxygen molecule than it did to bind to the first one
- This is called positive cooperativity because binding of the first molecule makes the binding of the second one easier and so on
- The gradient of the curve steepens
4.
- After the binding of the third molecule, the situation changes
- It becomes harder for the haemoglobin to bind to the fourth oxygen molecule
- This is simply due to probability
- With the majority of the binding sites occupied, it is less likely that a single oxygen molecule will find an empty site to bind to
- The gradient of the curve reduces and the graph flattens off
The many different oxygen dissociation curves are better understood if two facts are always kept in mind -
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