Haemoglobin Flashcards
What protein is involved in the transport of oxygen from the lungs to the tissues?
Haemoglobin
What can you use to determine concentration of something, and why?
spectrophotometer
The absorbance of a solution is proportional to the concentration of the absorbing material within it and to the distance (or path length) travelled by the light through the sample.
What is the Beer-Lamber law?
A= E x c x L
absorbance of the solution
concentration
path length
extinction coefficient
What is the extinction coefficient?
a constant for the substance being measured at that particular wavelength
What are the 2 main functions of haemoglobin?
to efficiently transport oxygen from the lungs to the tissues
help transport CO2 back to the lung
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
How is the binding of oxygen to haemoglobin described?
cooperative
- meaning that binding of one O2 molecule to a haem group results in a change in the conformation of other subunits, affecting their ability to bind O2
What type of effect is there in haemoglobin?
Positive cooperative effect
- meaning that as oxygen binds to one haem group, the affinity of the remaining haem groups for oxygen is increased
How is the positive cooperative effect shown?
Exemplified by the sigmoidal nature of the oxygen association curve for haemoglobin
Where in humans is the partial pressure of O2 approaching 100 torr, and the haemoglobin is almost completely saturated with oxygen (98%)?
The lungs
Why might some substances fail to obey the beer-lambert law?
for example, at high concentrations a protein might form dimers with a different extinction coefficient)
For hypothetical noncooperative oxygen transport protein, the maximum amount of oxygen that can be transported from regions with identical pO2 values is what, and what does it show?
38%
- shows that, positive cooperativity displayed by the binding of oxygen to haemoglobin enables it to deliver almost twice as much oxygen than would be possible in the absence of cooperativity
What is myoglobin?
an oxygen binding protein found in muscle, has one haem group per molecule and displays greater affinity for oxygen than haemoglobin
saturating at lower pO2 values
the lack of cooperativity means that it is poor at releasing oxygen under the same conditions
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