The sigmoid shape of the oxygen dissociation curve results from positive cooperativity: initially, binding is difficult, but the first O2 binding causes a shape change that facilitates subsequent binding, until saturation occurs at high O2 pressures.
At low partial pressure of O2 : - polypeptide sub units closely united - difficult for first O2 to bind to Fe2+ - small initial gradient - first O2 causes change in tertiary structure and shape - causes second and third O2 to bind to Fe2+ more easily - positive cooperativity - larger gradient At high partial pressure of O2: - 3/4 haemoglobin binding sites occupied - difficult for 4th O2 to bind to Fe2+ - curve levels off
| Front | Explain the sigmoid shape of an oxygen dissociation curve |
|---|---|
| Back | At low partial pressure of O2 : - polypeptide sub units closely united - difficult for first O2 to bind to Fe2+ - small initial gradient - first O2 causes change in tertiary structure and shape - causes second and third O2 to bind to Fe2+ more easily - positive cooperativity - larger gradient At high partial pressure of O2: - 3/4 haemoglobin binding sites occupied - difficult for 4th O2 to bind to Fe2+ - curve levels off |
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