Haemoglobin and Oxygen Dissocitation Curves

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HaemoglobinA group of protein molecules that have a quaternary structure. Four Structures: Primary Structure – Consisting of four polypeptide chains. Secondary Structure – In which each of the polypeptide chains is coiled into a helix. Tertiary Structure – In which polypeptide chain is folded into a precise shape in order to carry oxygen. Quaternary Structure – In which all four polypeptide chains are linked together in a spherical molecule. Each polypeptide is associated with a haem group (contains an Fe2+ ion). Each Fe2+ ion can combine with a single oxygen molecule, a total of four O2 molecules can be carried by a single haemoglobin molecule in humans. The role of haemoglobin is to transport oxygen. To be efficient it must: Readily associate with oxygen at the surface where gas exchange takes place. Readily dissociate from oxygen at those tissues requiring it. In the presence of carbon dioxide, the new shape of the haemoglobin molecule binds more loosely to oxygen; as a result haemoglobin releases its oxygen. Haemoglobins with a high affinity for oxygen. Takes up oxygen more easily but releases it less readily. Haemoglobins with a low affinity for oxygen. Takes up oxygen less easily and releases it more readily. Environment with little oxygen – organism has haemoglobin that readily binds with oxygen and a low metabolic rate. An organism with a high metabolic rate needs to release oxygen readily into tissues. Loading and Unloading Oxygen: Oxygen combines with haemoglobin in a process called loading or associating. (In the Lungs) Haemoglobin releases oxygen in


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