7.2 - Transport of Oxygen by Haemoglobin

• What is an oxygen dissociation curve?

  graph showing relationship between the saturation of haemoglobin with oxygen and the partial pressure of oxygen showing a cooperative binding process of oxygen
• cooperative binding process of oxygen

  shape of haemoglobin makes it hard for first oxygen to bind to a site on a polypeptide chain as they are very close so at low pO2 little oxygen binds to haemoglobin so loan saturation of O2

  after first of O2 binds the quaternary structure changes so haemoglobin changes shape making it easier for 2nd & 3rd Oxygens to bind so O2 binds at a smaller increase in pO2 - higher affinity

  after 3rd O2 binds it becomes harder for last O2 to bind as majority of binding sites are occupied so probability of Oxygen binding to an empty site is lower
• what does a leftward shift mean in an oxygen dissociation curve?

  haemoglobin has a greater affinity for oxygen so loads oxygen readily but unloads less easily
• what does a rightward shift in an oxygen dissociation curve mean?

  haemoglobin has a lower affinity for oxygen so loads less easily but unloads more easily
• oxygen dissociation curve for foetal hemoglobin vs human haemoglobin

  curve for foetal haemoglobin is shifted to the left of human haemoglobin

  so foetal haemoglobin has a higher affinity for oxygen so has a higher percentage saturation than adult haemoglobin
• why does foetal haemoglobin have a higher affinity for oxygen than human haemoglobin?

  allows foetus to obtain oxygen from its mother's blood at the placenta

  foetal haemoglobin birds to oxygen at low pO2 which is when mother's haemoglobin is dissociating with oxygen
• what's the effect of altitude on oxygen dissociation curves?

  causes a leftward shift as partial pressure of oxygen is lower due to lower atmospheric pressure so haemoglobin must have a higher affinity for oxygen so loading happens very readily allowing animals to obtain enough oxygen saturation in their blood
• lugworm dissociation curve

  live on seashore & obtain O2 from sea water which covers it most of the time

  curve shifts to the left so higher affinity for oxygen so loading happens even when pO2 is low as it decreases as lugworm uses oxygen in water
• Bohr effect

  rightward shift of oxygen dissociation curve to the right as pCO2 increases due to respiration Which reduces affinity of haemoglobin for oxygen because dissolved CO2 forms carbonic acid which lowers pH so alters ionic & hydrogen bonds in haemoglobin so changes the tertiary structure so haemoglobin changes shape so oxygen dissociates
• CO2 concentration at gas exchange surface

  low because it diffuses across exchange surface and leaves the body

  so affinity for oxygen increases and high pO2 in lungs means oxygen associates with haemoglobin

  Oxygen dissociation curve shifts to the left
• CO2 concentration in rapidy respiring tissue

  high as it's released by respiration so reduces affinity of haemoglobin for oxygen & low CO2 means oxygen dissociates into muscle cells

  oxygen dissociation curre shifts to the right
• factors that ensure there's enough oxygen for tissues

  CO2 is constantly removed so pH is higher so increases affinity for oxygen

  CO2 produced in respiring tissues so lowers pH so lower affinity for oxygen so unloads
• why is more oxygen unloaded in more active tissues?

  higher rate of respiration so more CO2 produced so lower pH so greater haemoglobin change in shape so oxygen is unloaded more readily so more oxygen available for respiration