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