Topic 8: Oxygen transporters Flashcards
what are the two molecules that transport oxygen
haemoglobin and myoglobin
what’s the difference between haemoglobin and myoglobin
haemoglobin - blood, my - muscle
transports oxygen v short term storage of O2
4 polypeptide chains v 1 polypeptide chain
4 haem groups per molecules v 1 haem group per molecule
why are molecules needed to transport oxygen
can not diffuse in aqueous solution - so transported around body
how does oxygen bind to haemoglobin
changes the position of the iron ion
the haem group is bound to polypeptide chain via a histidine group
shows a sigmoidal binding curve - affinity for oxygen increase with partial pressure of O2
how does oxygen bind to myoglobin
shows a hyperbolic dependence on oxygen concentrations - so a constant affinity for oxygen
why does oxygen more readily bind to myoglobin
due to structure
one single subunit in myoglobin
two alpha + two beta in haemoglobin
haemoglobin undergoes conformational change at the binding of oxygen
T state (deoxyhaemoglobin) -> R state (oxyhaemoglobin ) - allosteric effect. the binding of oxygen promotes transition from low affinity T state to high affinity R state
why is the sigmoidal properties of Hb good
allows greater oxygen transport compared to comparable proteins entirely in the high affinity R state or low affinity T state
using 66% of available binding sites in comparison to 7% for myoglobin
what are the regulators of oxygen binding (t state)
allosteric effectors:
1,2,3- bisphosphoglycerate in RBC’s - lowers the affinity of Hb for oxygen, stabilises T state, shifts curve to right
BGP interacts with the positively charged residues on each beta subunit - holding them together, stabilises form
CO2 and H+ (the bohr effect) - lowers affinity of Hb for oxygen, stabilises the T state, allows delivery of oxygen to metabolically active tissues that produce H+ and CO2
what are the regulators of oxygen binding (r state)
CO binds more readily than O2
blocks further oxygen binding - dead
stabilises R state in unaffected subunits - shifts curve to left, prevents dissociation at tissues
what are genetic diseases associated with oxygen transport
sickle cell disease
due to mutation of glutamate to valine in beta subunit, and puts hydrophobic patch on another beta subunit to interact with valine - so stick together
aggregation forms - usually goes on their own…more prone to lyse (anaemia) and more rigid (block microvasculature)
what are the different types of haemoglobin the blood
HbA 90%
HbF less than 2%
HbA2 - 2-5%
AS THERE IS MORE THAN ONE GENE THAT ENCODES FOR THEM - so different forms of beta globin
beta increases after birth, gamma high in young
due to higher binding affinity in HbF than HbA which allows foetal blood supply to have lots of oxygen, across placenta
