One molecule of haemoglobin can combine with
- A. one molecule of oxygen
- B. four molecules of oxygen
- C. two molecules of oxygen
- D. an unlimited number of oxygen molecules
Explanation
Haemoglobin has four polypeptide chains, each with an iron containing haem group that binds one oxygen molecule, giving a maximum of four. Binding is cooperative, so the attachment of the first oxygen makes the next ones easier, and this is what gives the oxygen dissociation curve its S shape. Full saturation is reached in the lung capillaries within a fraction of a second.
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