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Definition of haemoglobin

Molecule required to efficiently transport O2 from the lungs to respiring tissues


Definition of myoglobin

Stored in muscles, unload O2 at very low O2 partial pressures


Structure of haemoglobin

2a, 2b chains, 4 haem groups
Haem group has porphyrin ring (Fe2+/Fe3+), make 6 bonds
4 bonds with N, 1 bond with proximal histidine, last spot open for O2
Distal histidine binds to rest of globin


Myoglobin structure and properties

Monomeric haem found mainly in muscle
Facilitate O2 transport in rapidly respiring muscle
Receives O2 from Hb


Role of distal histidine in haemoglobin

Stabilises O2, déstabilises CO binding by reducing affinity


What happens when deoxyhaemoglobin forms

H2O displaces Fe center of haem down by O.4A


What happens when oxyhemoglobin forms

O2 binds to Fe center, moves back up into plane


Oxygen induced structural arrangements

O2 binds to open space in porphyrin ring, gains e- from Fe2+
Fe3+ has fewer electrons, ionic radius decreases, moves into plane of ring, decreased repulsion
Facilitates allosteric transition from T state to R state, changes affinity for O2 binding to subsequent haems, positive cooperativity


Relationship between O2 saturation and PO2 in myoglobin

Typical hyperbolic relationship
O2=PO2/P50 + PO2


Relationship between O2 saturation and PO2 in haemoglobin

+ve cooperative, more binds, easier to bind
Hba is further to the right than Hbf


CO2 and H+ transport in Hb in respiring tissues

CO2 + H2O =(carbonic anhydrase)=> HCO3- + H+
Bicarbonate dissolves in plasma, Cl- enters
Decreases affinity for O2


CO2 and H+ tranport in Hb in lungs

HCO3- + H+ =(carbonic anhydrase)=> CO2 + H2O
Bicarbonate exerts RBC, Cl- leaves
Increases affinity for O2


Bohr effect in tissues

At tissues, lower pH
Curve shifts to the right
Increased binding of CO2
Decreased affinity for O2


Opposite of the Bohr effect in lungs

Lungs, higher pH
Curve shifts to the left
Decreased binding of CO2
Increased affinity for O2


Structural determinants of Bohr effect

Deoxy => Oxytocin's, shifts equilibrium between T and R states
Increase in H+ conc favors T state, more O2 released, +ve feedback


What is the function of BPG and the effect of the cooperatively curve

Lowers affinity for O2 compared to pure Hb
At altitude, conc of BPG increases, decreases O2 affinity
Curve shifts to the right, more unloaded


How does BPG change O2 affinity

T state, favors O2 release
R state, favors O2 pickup
BPG stabilises T state, v lively charged, fits into +ve porphyrin ring
BPG can fit in the central pocket of tetramer


BPG and HbF

Made up of 2a, 2y chains
BPG stabilisation is less efficient than Hba
Results in higher O2 binding affinity of Hbf than Hba


What causes sickle cell anaemia

Glutamic acid (-ve) substituted by valine (non polar)
Creates hydrophobic sticky patches to normally charged B chains


What happens in sickle cell anaemia

When deoxygenated, aggregate into insoluble fibres
Fibres form as valine has a complementary shape to the hydrophobic pocket in chain
Fibres deform RBC into sickle shapes
Cells lyse, carrying capacity of O2 decreases, block up blood vessels


Types of haemoglobin present in the embryo



First haemoglobin present in the embryo



Haemoglobin most prevalent at birth