haemoglobin

• haemoglobin 


  the oxygen carrying component of blood
• haemoglobin is a complex protein which consists of 4 chains of polypeptide called globin
• the haem group is tuck din the centre of it and contains an Fe2+ ion at its centre which can combine with oxygen
• each molecule of human haemoglobin can carry 4 oxygen molecules
• In the lungs, oxygen joins to the iron in haemoglobin to form oxyhemoglobin which is a reversible reaction
• When an oxygen molecule joins to haemoglobin it's referred to as association or loading, and when oxygen leaves oxyhemoglobin it's referred to as dissociation or unloading.
• association and dissociation of haemoglobin

  A) haemoglobin

  B) oxygen

  C) loading

  D) unloading

  E) oxyhemoglobin

  F) Hb

  G) 4O2

  H) HbO8

  
• affinity of oxygen 


  the tendency a molecule has to bind with oxygen.
• partial pressure of oxygen (pO2)

  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 oxyhemoglobin where there's a high pO2
  • Oxyhemoglobin unloads its oxygen where there's a lower pO2
• • Oxygen enters blood capillaries at the alveoli in the lungs.
  • Alveoli have a high pO2 so oxygen loads onto haemoglobin to form oxyhemoglobin.
  • When cells respire, they use up oxygen - this lowers the pO2.
  • Red blood cells deliver oxyhemoglobin to respiring tissues, where it unloads its oxygen.
  • The haemoglobin then returns to the lungs to pick up more oxygen.
• oxygen loading and unloading in the body

  A) alveoli in lungs

  B) respiring tissue

  C) low

  D) low

  E) low

  F) unloads

  G) high

  H) high

  I) high

  J) loads

  
• dissociation curves 


  shows how saturated the hemoglobin is with oxygen at any given partial pressure.
• Where pO, is high (e.g. in the lungs), haemoglobin has a high affinity for oxygen, so it has a high saturation of oxygen.
• Where pO, is low (e.g. in respiring tissues), haemoglobin has a low affinity for oxygen, so it has a low saturation of oxygen.
• • When haemoglobin combines with the first O2 molecule, its shape alters in a way that makes it easier for other molecules to join too.
  • as the haemoglobin starts to become saturated, it gets harder for more oxygen molecules to join.
  • As a result, the curve has a steep bit in the middle where it's really easy for oxygen molecules to join, and shallow bits at each end where it's harder
  • When the curve is steep, a small change in pO2 causes a big change in the amount of oxygen carried by the haemoglobin.
• S-shaped dissociation curve for haemoglobin

  A) hard for oxygen molecules to load onto Hb

  B) very easy for oxygen molecules to load onto Hb

  
• organisms with less O2 in their environment such as fish need haemoglobin with a high affinity for oxygen
• animals with a high metabolic rate need haemoglobin with a low affinity for oxygen so its released more easily at the respiring tissues