4.5 transport of gases

• structure of haemoglobin?

  • globular
  • hydrophillic (water soluble)
  • 4 polypeptide chains containing haem groups
• function of haemoglobin?

  binds to oxygen at varying affinity to transport around body
• each of the 4 haem groups binds to oxygen - forming oxyhaemoglobin
• how does carbon dioxide transport occur?

  • hydorgencarbonate ions in the red blood cells
  • carbaminohaemoglobin (formed in reaction between co2 and amine groups in haemoglobin)
• oxygen disassociation curve of haemoglobin

  • s shaped curve - cooperative binding occurs
  • further left the curve, more affinity for oxygen

  
• high partial pressures

  • oxygen is loaded onto haemoglobin
  • therefore fully saturated
  • increase in affinity
• low partial pressure

  • oxygen unloaded
  • released into respiring tissue
  • lower affinity
• cooperative binding

  • after first molecule of oxygen binds,
  • its easier for 2nd and 3rd molecule to bind
  • its harder for the 4th to bind - low probability of oxygen binding to remaining haem group
• bohr effect

  • oxygen unloads more readily at higher carbon dioxide concentrations
  • because it forms carbonic acid in the blood
  • which lowers pH
• mark scheme explanation for change in oxygen disassociation graph

  • red has moved to left of b
  • as it has higher affinity to oxygen
  • because at the same partial pressure, red has a higher % saturation
  • oxygen loads more readily, unloads less readily
  • due to.... (e.g. exercise)

  
• foetal haemoglobin

  • higher affinity for oxygen compared to adults
  • therefore can load more oxygen from mother's haemoglobin
  • curve to the left of adult

  
• myoglobin

  • found in muscle tissue
  • high affinity for oxygen - only has 1 polypeptide chain so only 1 haem group
  • oxygen unloads from haemoglobin and binds to myoglobin in muscle cells
  • oxygen only unloaded from myoglobin at low partial pressure, when muscle cell is respiring rapidly
  • acts as oxygen store, makes oxygen available when needed
  • curve lies further left

  
• mouse

  • lose heat quickly - large sa:vol
  • need a high metabolic rate to generate more heat
  • high respiration rate = more co2
  • therefore ph reduced
  • oxygen is unloaded readily (due to bohr effect)
  • curve to the right