3.1.2j) The oxygen dissociation curve for fetal and human haemoglobin Flashcards
Oxygen dissociation curve
The percentage saturation haemoglobin in the blood is plotted against the partial pressure of oxygen (pO₂)
Shows the affinity of haemoglobin for oxygen
Curve levels out at the highest partial pressure as all haem groups are bound to oxygen - haemoglobin is fully saturated
Bottom portion of curve
At low pO₂, few haem groups are bound to oxygen - so haemoglobin does not carry much oxygen
Middle portion of curve
At higher pO₂ more haem groups are bound to oxygen making it easier for more oxygen to be picked up
Top portion of curve
The haemoglobin becomes saturated at very high pO₂ as all the haem groups become bound
Bohr shift (the effect of carbon dioxide)
As the partial pressure of CO₂ rises (higher partial pressure of CO₂) - haemoglobin gives up oxygen more easily
Bohr effect is important in the body
Active tissues - with a high partial pressure of CO₂, haemoglobin gives up O₂ more easily
In the lungs - proportion of CO₂ in the air is relatively low, O₂ binds to the haemoglobin molecules
Fetal haemoglobin
Fetus is dependent on the mother to supply it with O₂
Oxygenated blood from the mother runs close to the deoxygenated fetal blood in the placenta
Fetal blood has higher affinity for O₂ (at every point of the curve) to transfer O₂ to the fetus
Fetus removes O₂ from the maternal blood as they move past each other
Transporting carbon dioxide
5% - carried dissolved in the plasma
10-20% - combined with the amino groups in the polypeptide chains of haemoglobin (Carbaminohaemoglobin)
75-85% - converted into hydrogen carbonate ions in the cytoplasm of RBC
Carbonic acid reaction
CO₂ reacts slowly with water to form carbonic acid
Carbonic acid then dissociates to form H+ ions & hydrogen carbonate ions
Takes place in the blood plasma
In the cytoplasm of RBCs - high levels of carbonic anhydrase (catalyses the reversible reaction)
