Oxyen Transport Flashcards
What is myoglobin?
- a red protein containing haem , which carries and stores oxygen in muscle cells.
Why does oxygen actually need to bind to haemoglobin in order to be transported ?
Because oxygen is insoluble so it cannot merely just dissolve in blood and be transported
What does oxygen actually bind to in haemoglobin?
It binds to Fe2+ ions in the haem group.
How many o2 molecules can bind to one Fe2+ ion in each haem group , in both myoglobin and haemoglobin?
1 molecule of o2.
How is Fe2+ actually bound to the protein ?
Via a histidine residue ( proximal histidine ) on the other side of the ring
Describe the structure of myoglobin
- globular protein
- compact structure
- 75% alpha helical
- single chain globular protein that consists of 153 amino acids.
What type of graph would the binding of oxygen to myoglobin exhibit ?
- hyperbolic graph
- as myoglobin has a higher affinity for oxygen than haemoglobin
Explain how myoglobin slightly changes in conformation when oxygen binds ?
- Fe in deoxymyoglobin is slightly below the plane of the ring , when oxygen binds it causes movement of fe into the plane of the ring .
- movement of fe causes movement of histidine F8 and a small change in overall protein conformation
What best describes the shape of a oxygen -haemoglobin dissosiation curve ?
Sigmoidal
Describe the structure of haemoglobin
2 alpha helical subunits ( made up of 141 amino acid residues) and 2 beta subunits (146 amino acid subunits)
- 4 polypeptide chains in total
- can bind with 4 oxygen molecules.
What are the two states haemoglobin can exist as ?
- T state ( low affinity T state) - before any oxygen has bound
- high affinity R state - once oxygen has bounded to first haem group
Why is the oxygen binding curve for haemoglobin sigmoidal ?
- the binding of one oxygen molecule promotes the binding of subsequent molecules because it causes a conformational change in haemoglobin from a Low affinity T state to a high affinity R state.
- this makes it easier for haemoglobin to bind to oxygen,
- this is important because if haemoglobin remained in a high affinity state all the time then oxygen would be strongly bound and there would be less oxygen being unloaded for respiring tissues,
What are the two things that can help regulate oxygen binding ?
- 2,3 bisphosphoglycerate (BOG)
2) carbon dioxide and H+
What is the role of 2,3 biphophosphoglycerate
- it binds to an allosteric site on haemoglobin and works to reduce haemoglobins affinity for oxygen - this helps to regulate oxygen binding.
- it is an allosteric inhibitor
Why do athletes tend to train at high altitudes?
-athletes tend to train at high altitudes because at high altitudes there is very low oxygen in the atmosphere. This promotes the increase in the concentration of Biphospholglycerate. This results in a reduced affinity for oxygen , which results in greater oxygen release to tissues.
What is the resulting consequence of H+ and co2 binding to haemoglobin? and what is this called
Lowers the affinity of haemoglobin for oxygen
BOHR EFFECT
Why is the Bohr effect important ?
Metabolically active tissues produce large amounts of H+ and Co2 - Bohr effect ensures the delivery of o2 is coupled to demand.
Carbon monoxide poisoning
- this is where CO permenantly binds to haemoglobin and haemoglobin. This blocks oxygen transport. When 2/4 subunits are bound to carbon monoxide , it becomes lethal.
How would we treat carbon monoxide poisoning?
1) blood transfusions
2) place patient in a room that has a very high pressure of oxygen.
What are the three different forms of haemoglobin?
HbA : 2 alpha subunits and 2 beta subunits.
2) HbF ( foetal haemoglobin) : 2 alpha subunits and 2 gamma subunits
3) HbA2 : 2 alpha subunits and 2 delta subunits
When is the majority of alpha subunits formed in a human ?
Very early development, 9 months before baby is born.
When is the majority of beta subunits made ?
3 months after birth
Why is foetal haemoglobin so important .
HbF is the major haemoglobin in foetal blood.
- it has a higher affinity for o2 than HbA which allows transfer of o2 to foetal blood from the mother.
What is the cause of sickle cell anaemia
Missense mutation
- which results in glutamate being replaced by valine In Beta globin.
- it is now called HbS.
- glutamate is hydrophilic whereas valine is hydrophobic which results in deoxygenated HbS to interact with eachother and polymerise.
- this results is sickled cells : make prone to lyse ( anaemia )
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