Haemoglobin

All about haemoglobin

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Structure of haemoglobin molecules

  • Primary structure, consisting of four polypeptide chains.
  • Secondary structure, in which each of these polypeptide chains is coiled into a helix.
  • Tertiary structure, in which each polypeptide chain is folded into a precise shape - an important factor in its ability to carry oxygen.
  • Quaternary structure, in which all four polypeptides are linked together to form an almost spherical molecule. Each polypeptide is linked to a haem group.
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The role of haemoglobin

  • The role of haemoglobin is to transport oxygen.
  • To be effict at transporting oxygen, haemoglobin must:
    • readily associate with oxygen at the surface where gas exchange takes place
    • readily disociate with oxygen at those tissues requiring it
  • Haemoglobin changes its shape in the presence of certain substances, such as carbon dioxide
  • In the presence of CO2, the new shape of the haemoglobin molecule binds more loosely to oxygen, meaning it releases its oxygen
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Loading and unloading oxygen

  • The process by which haemoglobin combines with oxygen is called loading, or associating.
  • This takes place in the lungs.
  • The process by which haemoglobin releases its oxygen is called unloading, or dissociating
  • This takes place in tissues.
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Oxygen disocciation curves

  • The further to the left the curve is, the greater the affinity the haemoglobin has for oxygen
    • meaning it takes up oxygen readily but releases it less easily
  • The further to the right the curve is, the lower the affinity the haemoglobin has for oxygen
    • meaning it releases oxygen readily but takes it up less easily
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Effects of carbon dioxide concentration

  • The greater the concentration of carbon dioxide, the more readily the haemoglobin releases its oxygen (the Bohr effect).
  • At the gas-exchange surface (the lungs), the level of CO2 is low because it diffuses across the exchange surface and is expelled from the organism.
    • The affinity of haemoglobin for oxygen is increased
    • Oxygen is more readily loaded by haemoglobin
    • Reduced CO2 levels has shifted the dissociation curve to the left
  • In rapidly respiring tissues (e.g. muscles), the level of CO2 is high
    • The affinity of haemoglobin for oxygen is decreased
    • Oxygen is readily unloaded from the haemoglobin into the muscle cells
    • Increased CO2 levels has shifted the dissociation curve to the right
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Loading, transport and unloading of oxygen

  • At the gas-exchange surface, CO2 is constantly being removed.
  • The pH is raised due to the low level of carbon dioxide.
  • The higher pH changes the shape of the haemoglobin into one that enables it to load oxygen more readily.
  • This shape also increases the affinity of haemoglobin for oxygen, so it is not released while being transported in the blood to the tissues.


  • In the tissues, CO2 is produced by respiring cells.
  • CO2 is acidic in solution, so the pH of the blood within the tissues is lowered.
  • The lower pH changes the shape of haemoglobin into one with a lower affinity for oxygen
  • Haemoglobin releases its oxygen into respiring tissues
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Size matters

  • Mice are small animals and therefore have a large surface area to volume ratio.
  • As a result, they tend to lose heat rapidly when the environmental temperature is lower than their body temperature.
  • To compensate for this, they have a high metabolic rate that generates heat and helps to maintain their normal body temperature.
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Activity counts

  • Flights in birds and swimming in fish are both energy-demanding processes.
  • The muscles that move a bird's wings are powerful and require a lot of oxygen to allow them to respire at a sufficient rate to keep the body airborne.
  • Flight muscles have a very high metabolic rate and, during flight, much of the blood pumped by the heart goes to these muscles.
  • While birds use a great deal of energy opposing gravity in a medium that gives little support, fish have a different problem.
  • They expend considerable energy swimming through a medium that is very dense and therefore difficult to move through.
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Comments

Olivia

Found this really useful! Been struggling with it for a while so it gave me some great background knowledge to start muddling through it :) 

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