3.2 Haemoglobin Flashcards
What protein is involved in the transport of oxygen from the lungs to the tissues?
Haemoglobin
Describe the structure of haemoglobin?
- Consists of 4 globin chains
- Each globin chain contains a haem group
- Each haem group is has a central ferrous iron atom (fe2+) surrounded by a porphyrin ring
What four chains are HbA molecules made up from?
2 alpha chains and 2 beta chains
What two chain type is fetal haemoglobin made from?
2 alpha chains and 2 gamma chains
What is meant by the positive cooperative binding which oxygen displays?
As oxygen binds to Hb, a conformational change occurs in the other subunits
This increases the affinity of the other haem groups for oxygen, resulting in the sigmoidal O2 dissociation curve
How is the oxygen affinity different in fetal haemoglobin compared with adult haemglobin?
The oxygen affinity is higher
How does HbF have a higher oxygen affinity than HbA?
A single AA substitution results in reduced affinity for 2,3-DPG and therefore a higher oxygen affinity
Why is it essential that fetal haemaglobin has a high affinity for oxygen?
This means at very low concentrations of oxygen, which the placenta has, HbF can still readily bind the oxygen which the HbA is offloading
Why can myoglobin not display positive cooperativity?
It only has one oxygen binding site
What is the p50 value for myoglobin and haemaglobin respectively?
Myoglobin = 2
Hb = 26
Where is myoglobin found?
Predominantly in the muscle cells
Why is myoglobin useful?
It is a store of oxygen in muscles
It has a high oxygen affinity and only releases the oxygen it stores at low oxygen concentration
A right shift in the oxygen dissociation curve is associated with what change?
A decrease in the oxygen affinity
A left shift in the oxygen dissociation curve is associated with what change?
An increase in the oxygen affinity
What factors could cause an increase in the oxygen affinity (left shift)?
Decreased CO2, decreased 2,3-DPG, increased pH
What factors could cause a decrease in the oxygen affinity (right shift)?
Increased CO2, decreased pH, increased 2,3-DPG, increased temperature
Describe how a left shift in the oxygen dissociation curve results in an increase in the affinity for oxygen?
When the curve shifts left, the saturation of Hb is higher at the same partial pressure of oxygen
This is due to increased oxygen affinity thus Hb is less likely to release oxygen, hence being more saturated