haemoglobins

• when oxygen partial pressure is low, haemoglobin has a low affinity for oxygen
• As Po2 increases, affinity of haemoglobin for oxygen increases slightly
• When the first molecule of 02 binds to haemoglobin, the protein undergoes a conformational change, allowing the other o2 molecules to bind easier
• Plateau in percentage saturation:

  • as more o2 molecules bind to haemoglobin, it becomes more difficult for more to join
  • the percentage saturation begins to plateau
• As Po2 increases, percentage saturation of Hb increases, as o2 molecules bind easier. Then, the % saturation plateaus as it becomes harder for o2 to bind.
• when Pco2 is high, the rate of oxygen dissociation increases
• Bohr effect?

  • high co2 conc causes curve to shift to the right
  • affinity for oxygen decreases due to the acidic nature of co2 changing the shape of haemoglobin slightly
  • this means that oxygen will dissociate from haemoglobin at a lower po2 than normal
• Increase in carbon dioxide leads to increased hydrogen ion concentration which lowers blood pH
• Lowered pH makes it easier for oxygen to be released from haemoglobin
• structure of haemoglobin?

  • protein
  • quaternary structure
  • 4 polypeptide chains
  • each have 1 hem group which is where oxygen would bind
• what is meant by saturation of haemoglobin with oxygen?

  when haemoglobin is carrying the maximum amount of oxygen
• dissociation curve?

  • oxygen is loaded in regions with high partial pressure of oxygen (eg alveoli)
  • unloaded in regions of low partial pressure of oxygen (eg respiring tissues)
• high po2 = high affinity of o2
• low affinity = shifts right

  high affinity = shifts left
• Haemoglobins are protein molecules with a quaternary structure - they are made of 4 polypeptide chains. Each polypeptide is associated with a haem group containing a Fe2+ ion. Each Fe2+ can combine with a single oxygen molecule, making a total of 4 oxygen molecules carried.
• An oxygen dissociation curve shows the relationship between the saturation of haemoglobin with oxygen and the partial pressure of oxygen.
• A curve which is further to the left shows that the haemoglobin has a high affinity for oxygen, it will take it up more easily but release it less easily.
• A curve which is further to the right shows that the haemoglobin has a low affinity for oxygen, it will take it up less easily but release it more easily. Animals which use a lot of energy, such as fast swimming fish or birds in flight, will have a curve to the right of human haemoglobin. A mouse will also have a curve to the right, as it has a large surface area to volume ratio, and therefore a high respiration rate to maintain their body temperature.
• Haemoglobin has a lower affinity for oxygen in the presence of carbon dioxide, this is called the bohr effect. This is because dissolved carbon dioxide is acidic, it lowersthe pH and causes haemoglobin to change shape. This means that oxygen is more easily unloaded from haemoglobin in respiring tissues such as muscle cells.