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, HbA has 2 alpha chains and 2 Beta chains
- Each globin chain contains a haem group
- Each Haem group is made up from a central ferrous iron atom (fe2+) surrounded by a porphyrin ring
What four chains are HbA molecules made up from?
Two alpha chains and 2 beta chains
What two chain type is fetal haemoglobin made from?
Two alpha chains and two gamma chains
What is meant by the positive cooperative binding which oxygen displays?
This means that it becomes easier for oxygen to bind as more oxygen binds to it - hence resulting in the sigmoidal curve which arises when oxygen dissociation is plotted
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, which is mainly found in the muscles, and has a high affinity fr oxygen - it only releases the oxygen it is storing when the oxygen concentration is very low
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 shirt)?
Decreased CO2, Decreased 2,3-DPG, Decreased H+
What factors could cause a decrease in the oxygen affinity (right shift)?
Increased CO2, Increased H+, Increased 2,3-DPG and 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, at the same partial pressure of oxygen, the saturation of the haemoglobin molecules is higher. This is because as the affinity is higher, the Hb is less willing to release the oxygen molecules and therefore the Hb is more saturated
How is 2,3-DPG produced?
Rapoport-Leubering Shuttle
How does 2,3-DPG affect Hb?
it stabilises the structure and reduces the affinity for oxygen
what is the p50 value?
The value at which 50% of the oxygen molecules have bound
Why is Hb described as a tetramer?
because it has 4 globin chains
Describe what is meant by globin gene switching, and when does it occur?
Occurs at birth - this is the switch from gamma to beta chains, resulting in HbA not HbF
What is Carboxyhaemaglobin?
Molecule formed when carbon monoxide binds to Fe2+ int he haemoglobin
how does the affinity for CO2 differ from that of oxygen?
Much higher affinity for CO2 than O2
what is MetHb?
Methaemoglobin
How is MetHb generated?
Formed when Fe2+ ion is oxidsed to the ferric state
What is present if your blood has a blueish/chocolate colour?
Methaemoglobin
What enzyme is used to reduce methaemaglobin back to haemaglobin?
methaemoglobin reductase
What affect does MetHb have on oxygen?
MetHb can carry oxygen, however cannot release it to the tissues
What is Methaemaglobinaemia?
disorder where abnormal amounts of MetHb are produced
How can Methaemaglobinaemia be acquired?
Hereditary
Exposure to chemicals like aniline dyes, nitrates, benzene and benzocaine
What does the absorbance spectrum look like for oxy-haemoglobin?
There are two peaks, with one at 540
What is the ideal wavelength to set the haemoglobin absorbance spectrum at?
540nm
When is the spectrophotometry used clinically
To check the respiratory status of newborn babies
What is pulse oximetry?
A pulse oximeter is a non-invasive way of measuring oxygen saturation levels
Which is more negative HbA or HbS?
HbA is more negative
Why is HbS not as negatively charged as HbA?
A single point mutation occurs in the Beta chain of HbS - glutamate is replaced by valine
What affect does the single base substitution which occurs for HbS to form, have?
The substitution from Glutamate to Valine is one from
hydrophilic and negatively charged to hydrophobic and positively charged
What is the beer lambert Equation?
Absorbance = concentration of solute x light path x molar absorptivity
In gel electrohoresis, how can HbS be differentiated from HbA?
HbS is sickled Hb - this occurs due to a point mutation which is glutamate is replaced by valine (negative to positive).
Therefore, the HbS will be less negative and therefore not move as far towards the positive electrode as HbA will
Why do foetal red blood cells produce haemoglobin F rather than haemoglobin A?
Haemoglobin F has a higher affinity for oxygen than haemoglobin A which facilitates transfer of oxygen from the mother to the foetus.
How does chromatography on cellulose separate proteins?
on the basis of their charge
What is the role of the Rapoport–Luebering shuttle in red blood cells?
To generate 2,3-BPG which is important for the cooperative binding of oxygen to haemoglobin A.
