Haemoglobin

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Haemoglobin Molecules

Primary structure: Sequence of amino acids in the four polypeptide chains.

Secondary structure: Polypeptide chains coiled into a helix.

Tertiary structure: Polypeptide chain folded into precise shape to carry oxygen.

Quaternary structure: Four polypeptides linked forming spherical molecule. Haem group contains Fe2+ ion. Each of these ions combine with a single O2 molecule. Each haemoglobin therefore carries 4 O2 molecules.

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Loading and Unloading of Oxygen

Loading: Process of haemoglobin binding with oxygen. Takes place in lungs.

Unloading: Process of haemoglobin releasing oxygen. Takes place in tissue.

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Role of Haemoglobin

Haemoglobin’s role is to transport oxygen. In order to do this effectively:

 It needs to be able to readily associate with oxygen at gas exchange surfaces, and readily dissociate with oxygen at tissues requiring it.

Shape of oxygen changes depending on its environment and surrounding substances, which in turn chances its affinity for oxygen.

With CO2 present, haemoglobin binds more loosely to oxygen, losing affinity and releasing oxygen.

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Different Haemoglobins

Different organisms containing haemoglobin take up and release oxygen in different ways.

Each species’ haemoglobin has a different structure, due to acid sequence in the primary structure, causing for a slightly different tertiary and quaternary structure which cause for different oxygen binding properties; i.e. higher or lower affinity.

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