AQA Biology Haemoglobin

Structure
1. 4 sub-units
2. Each sub-unit contains a protein chain (globin) and a haem group (prosthetic).
3. The haem group contain ferrous ions (Fe 2+)
4. Protein with a quaternary structure
Role of Hb
1. Oxygen can bind to haemoglobin in the lungs and be transported round the body in the blood
2. Oxygen can dissociate with haemoglobin at respiring tissue muscle when in limited supply
Partial Pressure
1. Oxygen concentration is expressed as partial pressure (kilopascals)
2. The percentage of Hb associated with Hb at a given partial pressure is called percentage saturation
Affinity
1. The degree to which Hb binds with oxygen
2. A high partial pressure (e.g in lungs) means there is a higher affinity for oxygen
  1. Oxygen is therefore readily taken up
3. A low partial pressure (e.g in respiring tissue) the affinity for oxygen is low
  1. Oxygen is therefore readily released
Bohr Effect/Shift
1. In the presence of CO2, the affinity for oxygen is lower
  1. Oxygen is readily released when there is a high concentration of CO2
2. In lungs - low conc. of CO2 - increased affinity for O2 - promotes loading
3. In respiring tissue - high conc. of CO2 - decreased affinity for O2 - promotes unloading
4. Increased CO2 level causes the curve to shift the right
Oxygen Dissociation Curves
1. 0 p O2 - no oxygen bound to Hb
2. At low p O2 - polypeptide chain is tightly packed - harder for oxygen to bind to iron ions - curve rises gently
3. As one molecule of O2 binds to one haem group, polypeptide chain opens up - other 3 groups exposed - easy for oxygen to bind - curve rises steeply
4. High p O2 - Hb becomes saturated - curve plateaus

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AQA Biology Haemoglobin

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