Haemoglobin

• What is haemoglobin?


  A protein with a quaternary structure. It is evolved to make it efficient to load oxygen under one set of conditions but unloading it under a different set of conditions.
• Haemoglobin has four subunits, two alpha chains and two beta chains
• quaternary structure of haemoglobin

  All 4 polypeptide are linked forming a spherical molecule, each polypeptide associates with a haem group containing Fe2+, each Fe2+

  ion can combine with a single oxygen molecule so 4 oxygen can be carried via a single haemoglobin
• Role of haemoglobin and what factors allow this to occur

  To transport oxygen and for haemoglobin to do this

  1. Readily associates with oxygen at gas exchange surface
  2. Readily dissociates with oxygen at tissues requiring it
• How to achieve both contradictory factors of haemoglobin?

  Haemoglobin changes affinity via shape of protein changing at presence of certain substances e.g carbon dioxide.

  Presence of CO2 = Shape of haemoglobin binds more loosely to oxygen as a result haemoglobin releases oxygen
• Loading and unloading oxygen

  Loading - process of haemoglobin binding with oxygen (in lungs)

  Unloading - process of haemoglobin releases oxygen (in tissues)
• Temperature - temperature also affects the shape of haemoglobin. As temperature increases, the shape of haemoglobin changes causing it to become less able to bind with oxygen. Therefore, if we exercise our muscles produce heat which raises the temperature of the muscle cells. This makes it harder for haemoglobin to pick up oxygen from the bloodstream. However, the increase in temperature also stimulates breathing rate increasing the amount of oxygen available to the muscles.
• Haemoglobin with a high affinity of oxygen take up oxygen more easily but release oxygen not as easily

  Low affinity of oxygen = takes up oxygen less easily but releases it easily
• Why are there different haemoglobin?

  Each species produce haemoglobin with a slightly different amino acid sequence. Haemoglobin of each species have different tertiary and quarentary structure = different binding properties.

  Dependant on structure, haemoglobin molecules range from high to low oxygen affinity.
• How does affinity of oxygen for haemoglobin vary dependant on partial pressure of oxygen?

  As oxygen partial pressure increases, oxygen affinity increases, oxygen binds to haemoglobin tightly (loading)
• What occurs during respiration?

  Oxygen is used up so partial pressure decreases therefore affinity of oxygen for haemoglobin decreases so oxygen is released into respiring tissues
• What happens after unloading

  Haemoglobin returns to lungs where it binds to oxygen again