Haemoglobin and Oxyhaemoglobin
- Human haemoglobin is found in red blood cells - it carries oxygen around the body.
- It is a large protein with a quaternary structure - it has four polypeptide chains. Each chain has a haem group which contains iron and gives it it's red colour.
- Each molecule can carry four oxygen molecules.
- In the lungs, oxygen joins to the iron to form oxyhaemoglobin.
- This is a reversible reaction.
- When an oxygen molecule joins it is known as association or loading. and when it leaves it is dissociation or unloading.
Affinity for Oxygen and pO2
- Affinity means the tendency a molecule has to bind.
- The affinity varies depending on the conditions - one being the partial pressure of oxygen (pO2)
- This is a measure of oxygen concentration.
- The greater the concentration of dissolved oxygen in cells, the higher the partial pressure.
- As pO2 increases, haemoglobin's affinity for oxygen increases:
- Oxygen loads onto haemoglobin to form oxyhaemoglobin when there's high pO2.
- Oxygen enters blood capillaries at the alveoli in the lungs.
- Alveoli have a high pO2 so oxygen loads onto haemoglobin to form oxyhaemoglobin.
- When cells respire, they use up oxygen - lowering pO2.
- Red blood cells deliver oxyhaemoglobin to respiring tissues, where it unloads its oxygen.
- The haemoglobin then returns to the lungs to pick up more oxygen.
- Shows how saturated the haemoglobin is with oxygen at any given partial pressure.
- The affinity of haemoglobin affects its saturation.
- Where partial pressure is high, haemoglobin has a high affinity…