haemoglobin

• Haemoglobin gives red blood cells their pigment, they can carry up to 4 molecules of O2. it is a quaternary, globular protein made of 4 polypeptide chains. It associates and dissociates with O2 and contain iron in a haem group. 
• Oxygen uptake temporarily changes the shape of the protein meaning further O2 molecules can bin. This makes oxyhaemoglobin (HbO8). When oxygen is given up the normal protein shape returns, making deoxyhaemoglobin. 
• When there is a high concentration of oxygen Hb combines with oxygen to make oxyhaemoglobin. When blood reaches tissues which have low concentrations of oxygen, the Hb dissociates with the oxygen to release it into the tissues. 
• At high partial pressure of oxygen, Hb has a high affinity for oxygen, so associates with it easily. 
• At low partial pressure of oxygen, Hb has a low affinity for oxygen so finds it difficult to associate with it. 
• When blood moves around the circulation, it passes through areas of low partial oxygen so the oxygen it carries will be dissociated with it. This is useful because respiring tissues have low partial pressure because they have used it. Hb delivers more by dissociating with it where oxygen is needed. 
• The Bohr effect is when CO2 dissolves in the blood plasma and lowers the pH because it forms a weak acid. The weak acid alters the tertiary structure of Hb and causes oxygen to dissociate with oxygen, this allows more oxygen to be delivered to vary active respiring tissues.