3.2.7 transport of oxygen
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affinity
strong attraction
dissociation
releasing oxygen from oxyhaemoglobin
fetal haemoglobin
type of haemoglobin usually only found in foetus
haemoglobin
red pigment used to transport oxygen in blood
erythrocytes
red blood cells
describe the structure of haemoglobin
• complex protein with 4 subunits • each subunit = polypeptide chain & haem group • haem group contains single iron ion (Fe2+) • iron ion attracts/holds single oxygen molecule (high affinity for oxygen) • haemoglobin molecule only carry 4 oxygen molecules
describe the reversible binding of oxygen by haemoglobin
• association (binding) of haemoglobin & oxygen occurs in lungs where partial pressure (concentration) of oxygen is high • dissociation of haemoglobin & oxygen occurs in tissues where partial pressure (concentration) of oxygen is low
describe the transport of oxygen in lungs to tissues
• oxygen absorbed into blood as passes alveoli (lungs) • oxygen molecules diffusing into blood plasma diffuse into RBC • in RBC, oxygen becomes associated with haemoglobin (oxygen binds reversibly) • takes oxygen molecules out of solution = high concentration gradient in lungs • blood carries oxygen from lungs to heart & travels around body to tissues • in tissues, cells require oxygen for aerobic respiration = oxyhaemoglobin release oxygen via dissociation
another name for partial pressure of oxygen (pO2)
oxygen tension
what is partial pressure of oxygen (pO2) measured in
kPa
describe the haemoglobin dissociation curve 3 steps - 1) low oxygen tension, 2) oxygen tension increases & 3) haemoglobin approaches 100% saturation
• haemoglobin associates with oxygen to produce s-shaped curve • low oxygen tension = haemoglobin doesn’t readily associate its oxygen molecules as haemoglobin groups at centre of haemoglobin = oxygen cannot easily reach haem group & associate = low saturation level of haemoglobin • oxygen tension increases = diffusion gradient into haemoglobin increases = 1 oxygen molecule enter & associates with 1 haem group = slight change in haemoglobin molecule (conformational change) = allows more oxygen molecules to enter haemoglobin molecule & associate with other haem groups = steepness of curve • haemoglobin approaches 100% saturation = curve levels off causing s-shaped curve
compare adult & fetal haemoglobin (dissociation curves)
• fetal haemoglobin has higher affinity for oxygen = haemoglobin dissociation curve for fetal haemoglobin is to left of adult haemoglobin why? —> fetal haemoglobin must associate with oxygen in environment where oxygen tension is low enough to make adult haemoglobin dissociate –> in placenta (oxygen tension is low), fetal haemoglobin will absorb oxygen from surrounding fluid = reduces oxygen tension further –> as a result, oxygen diffuses from mother’s blood fluid into placenta = reduces oxygen tension within mothers blood –> causes maternal haemoglobin to dissociate further