Haemoglobin and Myoglobin Flashcards
Why doesn’t oxygen dissolve well in aq or water solutions?
Because it’s not a very polar molecule
What is the result of oxygens inability to dissolve well?
It cannot travel in the bloodstream
What happens as organisms get larger?
Need to find an effective mechanism of transporting oxygen
What is present in muscle?
Myoglobin
What does myoglobin do?
Accepts oxygen from haemoglobin
What does oxygen bind to?
Haem groups (not amino acids directly)
What does haem consist of?
Protoporphyrin ring, and Fe atom bound to 4 N atoms of ring
What part of the haem group is important?
Only the Fe, the rest just holds it in the ring
How many additional bonds can Fe 2+ make?
2- one on either side of the plane
What is Fe 2+ covalently bonded to in haemoglobin?
The protein
What is the result of Fe 2+ being covalently bonded to protein in haemoglobin?
Only 1 molecule of oxygen binds
How many molecules of oxygen bind in myoglobin?
1
How is the Fe atom bound to the protein?
Via a histidine residue on the other side of the ring
What is the histidine residue that the Fe atom binds to known as?
The proximal histidine
How many amino acids are there in myoglobin?
153
Is myoglobin compact or loose?
Compact
What % of myoglobin is made up of α-helixes?
75%
In myoglobin, which histidine is linked to the Fe atom?
His93
Where is the Fe in deoxymyoglobin?
Slightly below the plane of the ring
What does oxygen binding cause in myoglobin?
Movement of the Fe upwards, into the plane of the ring
What does the movement of Fe upwards in myoglobin cause?
Movement of His18, and a small change in overall protein conformation
Is the change in protein confirmation on oxygen binding important?
No
What relationship does oxygen binding to myoglobin show to oxygen concentration?
Hyperbolic
What can we tell from the hyperbolic binding curve of myoglobin binding and concentration of oxygen?
Myoglobin has save affinity to oxygen all the way through
What binding relationship does haemoglobin show against concentration of oxygen?
Sigmoidal
What is haemoglobin affinity for oxygen at low partial pressures?
Low
What happens to haemoglobins affinity for oxygen as partial pressure increases?
It increases
How many different types of polypeptide chain are there in haemoglobin?
2
What are the two different polypeptide chains in haemoglobin?
- α
- ß
How many amino acids are there in the α chain of haemoglobin?
141
How many amino acids are there in the ß chain of haemoglobin?
146
What conformation is adult haemoglobin in?
α 2 ß 2 tetramer
What is meant by aα 2 ß 2 tetramer?
There are 2 α chains and 2 ß chains
What does each polypeptide chain in haemoglobin have?
An essential haem prosthetic group
In what states does deoxyhaemoglobin exist?
- Low affinity T state
- High affinity R state
What does oxygen binding promote?
Stabilisation of the R state
What is the difference between the T and the R state?
From the T to the R state, the molecule has twisted round ~18º, which means histidines and negatively charged groups make interactions, which holds the molecule in high affinity. The haem group is now more exposed
What is the result of the haem group being more exposed?
It can bind to oxygen more easily
What happens when oxygen binds to haemoglobin?
The ferrous atom is pulled into the centre
What is the result of the pulling of the ferrous atom into the centre?
It pulls the entire sub unit, which has an effect on the entire molecule
What is the effect on the molecule of the movement of the ferrous ion on binding with oxygen?
It moves some amino acids, promoting being pulled into the high affinity state
What is meant by ‘co-operative binding’?
When binding of one oxygen molecule promotes the binding of subsequent oxygen molecules
What does the sigmoidal binding curve of haemoglobin mean?
That oxygen can be efficiently carried from the lungs to the tissues
Is it easy or hard for haemoglobin to take its first oxygen?
Hard
What happens once 1 oxygen molecule is binded?
Conformation changes to make subsequent binding easier
Is the partial pressure of oxygen in the lungs high or low?
High
What does the high p.p of oxygen in the lungs promote?
Binding of oxygen to haemoglobin molecules
Is the partial pressure of oxygen in the tissues high or low?
Low
Why is the partial pressure of oxygen in the tissues low?
Because other tissues have used the oxygen in the tissues to respire
What does haemoglobin need to do at the tissues?
Change its affinity
What is the ability of oxygen to change it’s affinity known as?
Co-operativity
What is the advantage of co-operativity?
More oxygen can be transported, as more is picked up at the lungs and then more released in tissues
What molecules are used to regulate oxygen binding?
- 2,3-bisphosphoglycerate (2,3-BPG)
- CO 2 and H +
What is the problem with oxygen under normal conditions?
It’s too effective to work
How is haemoglobins affinity to oxygen different without 2,3-BPG?
It’s higher
What does 2,3-BPG do to the binding curve of haemoglobin?
Moves it to the right
What does 2,3-BPG act as?
An allosteric inhibitor
Where does 2,3-BPG come from?
It’s a byproduct of glycolysis
At what concentration is 2,3-BPG present in RBC’s?
~5mM
How much 2,3-BPG binds per haemoglobin tetramer?
1
How does 2,3-BPG bind to haemoglobin?
The negatively charged phosphate binds to positively charged amino acid in ß sub units
How does 2,3-BPG concentration change at high altitudes?
It increases
Why does 2,3-BPG change at high altitudes?
To promote oxygen release at tissues
What affect does the binding of CO 2 and H + have on haemoglobin?
It lowers the affinity of haemoglobin for oxygen
What is the effect CO 2 and H + has on haemoglobin known as?
The Bohr effect
What happens when CO 2 dissolves in water?
It gives carbonic acid
What happens to carbonic acid in solution?
It dissociates to give H +
What do metabolically active tissues produce?
Large amounts of H + and CO 2 , and acidic metabolic intermediates
What does the Bohr effect ensure?
Delivery of oxygen coupled to demand
How does the Bohr effect ensure delivery of oxygen is coupled to demand?
If tissues are working hard, they make more CO 2 and acidic intermediates, so lower affinity, so oxygen given up more.
Hard working tissues require more oxygen
When is CO produced?
In the incomplete combustion of gas
Why is CO a poison?
Because it combines with ferromyoglobin and ferrohaemoglobin, blocking oxygen transport
How does the binding of CO to haemoglobin differ to that of oxygen?
CO binds 250x more readily
What does CO act as?
A competitive inhibitor
What happens once CO has binded?
It doesn’t come off under normal physiological circumstances
When is CO poisoning fatal?
When COHb >50%
What happens at COHb >50%?
Makes haemoglobin change confirmation so theres a higher affinity in unaffected subunits
Why is the increased affinity caused by CO fatal?
It means that oxygen will be taken up at the lungs, but not released at the tissues
What is the treatment for CO poisioning?
- Hyperbaric chamber
- In extreme cases, blood transfusions
How does a hyperbaric chamber work?
It increases oxygen concentration, and so increasing oxygen saturation in the lungs
What are the 3 types of normal adult haemoglobins?
- HbA (α 2 ß 2 )
- HbF (α 2 γ 2 )
- HbA 2 (α 2 δ 2 )
How do different types of haemoglobin differ from one another?
The ß sub-unit is replaced with something else
What % of haemoglobin is HbA?
90%
What % of haemoglobin is HbF?
What % of haemoglobin is HbA 2 ?
2-5%
What does glycosylation of HbA form?
HbA 1C
When is expression of different α- and ß- globin genes regulated?
During development
What is the result of gene expression?
Different genes are expressed at different points of life
Where are the globin genes that express different globin sub-units?
On 2 different locations on 2 different chromosomes
- On chromosome 16, 2 α like genes
- On chromosome 11, 2 ß sub units
What is HbF?
Fetal haemoglobin
Where is foetal haemoglobin the major type?
In foetal blood
How does HbF differ from HbA?
Higher binding affinity
What does the higher binding affinity of HbF allow for?
Transfer of oxygen to the foetal blood supply from the mothers
What must be the case for transfer of oxygen from maternal to foetal blood?
The foetal haemoglobin must be of higher affinity
What is sickle cell haemoglobin known as?
HbS
What is sickle cell anaemia a mutation of?
Glutamate (negative amino acid) to valine (neutral, hydrophobic) in ß globin
Why is the mutation in HbS significant?
Glutamate normally sits on the surface and is happy to interact with water. If mutated, valine is hydrophobic, so haemoglobin sticks 2 ß sub units together to exclude water
What is formed as a result of the mutation in HbS?
A sticky hydrophobic pocket formed by valine
What does the sticky hydrophobic pocket in HbS allow?
Deoxygenated HbS to polymerise
What are sickled cells more prone to?
Lyse
What does the lysis of blood cells lead to?
Anaemia
How to HbS cells differ from normal cells in terms of flexibility?
They are more rigid
What is the result of the rigidity of HbS cells?
They block microvasculature
What is produced when sickled cells stick together?
Abnormal chains
Do sickled cells work as oxygen transporters?
No
What happens to the sickled cells chains?
They clump together and bind to the cell membranes
What is the result of sickled cells binding to cell membranes?
They make the membranes much more rigid
What property to RBC’s usually have?
They’re usually squashy
What is the importance of the squashiness of RBC’s?
They can fit through capillaries
What is the result of sickled cells not having the squashy quality of normal RBC’s?
When they try and get through capillaries, they either block of lyse
What happens when sickled cells block vessels?
Painful symptoms
What are thalassaemias?
A group of genetic disorders that result from an imbalance in α- and ß- globin chains
What is normally the ratio between α and ß globin chains?
01:01
How many an imbalance between α and ß globin chains arise?
NAME?
What are ß-thalassemias?
When there is decreased/absent ß-globin chain production
What is the problem with ß-thalassemias?
α-chains are unable to form stable tetramers
What happens if not enough ß sub units are being made?
Excess α can precipitate out
Can a 4 α sun unit transport oxygen?
No
When do symptoms of ß thalassaemias appear?
After birth
What do the different forms of ß-thalassaemias depend on?
How many forms are absent
What is thalassaemia minor?
When one form is missing/mutated
What is thalassaemia major?
When both forms are missing/mutated
What is HbBarts?
When haemoglobin is formed purely fromγ sub-units
What are α-thalassemias?
When there is decreased/absent α-globin chain production, resulting in excess ß sub units
What are the levels of severity of α thalassaemias due to?
Multiple copies of the α chain being present
Can ß chains form stable tetramers?
Yes
How do ß chain tetramers differ from normal ones?
They have a higher affinity
What is the problem with the higher affinity of ß chain tetramers?
They pick up oxygen, but won’t release it
When is the onsets of α thalassaemias?
Before birth
