Haemoglobin

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  • Haemoglobin
    • Job
      • 1) Red blood cells contain haemoglobin
      • 2) Large protein w/ quarternary structure- made up of four polypeptide chains
      • 3) Each chain has haem group- contains iron ion, gives haemoglobin red colour
      • 4) Has high affinity for oxygen- each molecule can carry four O2 molecules
      • 5) In lungs, O2 joins haemoglobin to form oxyhaemoglobin
      • 6) Reversible reaction- when O2 dissociates from oxyhaemoglobin at body cell, turns back into haemoglobin
    • Partial Pressure
      • 1) Partial pressure of O2 is O2 concentration. Greater conc of O2= higher partial pressure
      • 2) Same for CO2
      • 3) Haemoglobin has a high affinity for oxygen when the partial pressure is high (loads) and vice versa (unloads)
      • 4) O2 enters blood capillaries at alveoli in lungs. Alveoli have high partial pressure, so O2 loads onto haemoglobin
      • 5) When cells respire, they use up oxygen. Lowers partial pressure- oxygen unloaded at respiring cells
      • 6) Haemoglobin returns to lungs to pick up more O2
    • Dissociation Curve
      • Where pO2 is high (lungs) haemoglobin has high affinity for O2- will readily combine. High saturation
      • Where pO2 low (respiring tissue) haemoglobin has low affinity for O2, unloads oxygen. Low saturation
      • S shaped: Haemoglobin binds with first O2 molecule, shape alters to make it easier for other molecules to join.
      • As Hb gets saturated, becomes harder for more molecules to join. Steep in middle of curve (easy to join) , shallow at each end (hard to join)
    • CO2 Concentration
      • Haemoglobin gives up O2 more readily at higher pressures of CO2
      • 1) Respiring cells produce CO2, raises pCO2
      • 2) Increases rate of O2 unloading- dissociation curve shifts to the right- saturation of blood w/O2 lower for given partial pressure, more oxygen being released
      • 3) Bohr effect
    • Different haemoglobin
      • Different organisms have different types of haemoglobin with different oxygen transporting capacities
      • 1) Organisms in environment with low conc of O2 have haemoglobin with higher affinity for O2 than humans- curve falls to left
      • 2) Very active organisms with high O2 demand have haemoglobin with a lower affinity for O2 than humans- curve to right of human one

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