Haemoglobin

  • protein - quaternary structure

    • structures - specific sequence of amino acids, folded + coiled, more folding, four strands (four polypeptide chains, each bonded to haem group (bound with iron ion - so can bind to four oxygen molecules in total))

  • varies throughout organisms

  • within red blood cells

  • carry oxygen to respiring tissues

  • two faced - behaves dependent on location (lungs or respiring tissue) allow it to change shape (for different properties)

  • load oxygen in lungs

    • higher affinity - binds easily - high concentration of oxygen

  • unload (dissociate) in respiring tissue

    • low oxygen - higher concentration of carbon dioxide - lower affinity (wants to let go)

  • high partial pressure - lots of oxygen (higher affinity - form oxyhaemoglobin in alveoli)

  • low partial pressure - less oxygen (lower affinity - dissociates oxygen)

  • Dissociation curve

    • start - low concentration - partial pressure increase - low affinity - binding sites closed off - haemoglobin changes shape to expose more binding sites when binding to first oxygen

    • steep curve - as first bond occurs, second gets easier then third gets easier (positive-cooperativity) however…

    • curve + plateau - no oxygen - shape of haemoglobin doesn’t expose all binding sites initially (difficult to find last binding site)

  • Bohr effect

    • oxygen in environment

    • alveoli - less carbon dioxide - less acidic (pH effects shape- easier for oxygen to load) - higher pH = higher affinity for oxygen (curves shifts left)

    • oxygen used up in cells - carbon dioxide builds up in cells - more acidic so lower pH = lower affinity for oxygen (haemoglobin unloads oxygen easier) - (line shifts right)

    • organisms in different environments

      • in low oxygen environment, an organism’s haemoglobin has higher affinity for oxygen in low oxygen conditions to load any available oxygen - dissociation curve shifted to the left

      • active organisms have lower affinity for oxygen to unload oxygen to respiring cells that need it - dissociation curve shifts to right

      • developing foetus - more efficient at loading oxygen in low oxygen concentrations - mothers blood lower in oxygen concentrations then air in alveoli