Unit 1 Section 5.5 Haemoglobin
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- Created on: 18-04-14 16:03
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- Haemoglobin
- Haemoglobin and oxyhaemoglobin
- human haemoglobin is found in red blood cells, its role is to carry oxygen around the body.
- Haemoglobin is a large protein with a quaternary structure - its made up of four polypeptide chains
- each chain has a haem group which contains iron and gives haemoglobin its red colour
- each molecule of human haemoglobin can carry four oxygen molecules
- in the lungs, oxygen joins to the iron in haemoglobin to form oxyhaemoglobin
- this is a reversible reaction - near the body cells, oxygen leaves oxyhaemoglobin and it turns back to haemoglobin
- when an oxygen molecule joins to haemoglobin its referred to as association or loading, and when oxygen leaves oxyhaemoglobin its referred to as dissociation or unloading
- this is a reversible reaction - near the body cells, oxygen leaves oxyhaemoglobin and it turns back to haemoglobin
- Affinity for Oxygen and pO
- affinity for oxygen means the tendency a molecule has to bind with oxygen
- haemoglobin's affinity for oxygen varies depending on the conditions its in - one of the conditions that affects it is the partial pressure of oxygen (pO )
- pO is a measure of oxygen concentration. the greater the concentration of dissolved oxygen in cells, the higher the partial pressure
- as pO increases, haemoglobin's affinity for oxygen also increases
- Oxygen loads onto haemoglobin to form oxyhaemoglobin where theres a high pO
- Oxyhaemoglobin unloads its oxygen where there's a lower pO
- Dissociation Curves
- an oxygen dissociation curve shows how saturated the haemoglobin is with oxygen at any given partial pressure
- the affinity of haemoglobin for oxygen affects how saturated the haemoglobin is
- fetal Haemoglobin
- adult haemoglobin and fetal haemoglobin have different affinities for oxygen
- Fetal haemoglobin has a higher affinity for oxygen than adult haemoglobin
- Carbon Dioxide Concentration
- the partial pressure of carbon dioxide (pCO ) is a measure of the concentration of CO2 in a cell
- to complicate matters, pCO also affects oxygen unloading. haemoglobin gives up its oxygen more readily at a higher pCO .
- its a cunning way of getting more O2 to cells during activity
- when cells respire they produce carbon dioxide which raises the pCO2
- this increases the rate of oxygen unloading - the dissociation curve 'shifts' right. the saturation of blood with oxygen is lower for a given pO2 meaning that more oxygen is being released. this is called the BOHR EFFECT.
- The Bohr Effect
- the reason for the bohr effect is linked to how CO2 affects blood pH
- most of the CO2 from respiring tissues diffuses into red blood cells and is converted to carbonic acid by the enzyme carbonic anhydrase
- the carbonic acid splits up to give hydrogen ions and hydrogencarbonate ions
- Haemoglobin and oxyhaemoglobin
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