Oxygen and Hemoglobin

To the tune of "Me and the Sky" from Come From Away
Tetrameric protein
That binds to oxygen
Allosterically modulated
The binding at one site affects how things can bind at another
Hemoglobin is why our blood red is in colour
Four heme groups that use iron as a cofactor
1.5% of O2 is dissolved physically
98.5 is combined chemically
Hemoglobin changes the blood's ability
To carry O2, it is highly increased
A unit consists of a heme ring structure
And a globin polypeptide chain
2α, 2β make up one up protein
The globin binds CO2, protons, and phosphates
The formation of
Oxyhemoglobin
Is promoted by the high
Partial pressures
Blood passes the respiratory surface
Partial pressure is high
This pressure difference means that almost all of the
Binding sites are occupied
Blood passes through the systemic tissues
Partial pressure is low
This pressure difference is what causes O2 to offload
Different modulators
Act in differing ways
O2 is a positive one
But CO2 and protons are not the same
They act as negative modulators for oxygen binding
And reduce the affinity
An increase in temperature as well weakens the bond between O2 and Fe
O2 affinity
Is quantified by the P50
The partial pressure of oxygen
That fills 50% of all of the binding sites on hemoglobin
Blood passes the respiratory surface
Partial pressure is high
This pressure difference means that almost all of the
Binding sites are occupied
Blood passes through the systemic tissues
Partial pressure is low
This pressure difference is what causes O2 to offload
The O2 dissociation curve has a sigmoidal shape
Flat region on top
Provides a safety net
When arterial pO2 falls too low
The Bohr shift improves offloading
Of O2 during exercise
An increase in venous pCO2
Shifts the curve to the right
H+ increases from lactic acid
A decrease occurs in venous pH
This shifts the curve to a higher p50
And more O2 is released
The transport of CO2 in the bloodstream
Is a slightly more complex process
10% is dissolved in the plasma
60% as bicarbonate
The reaction is catalyzed by carbonic anhydrase
Partial pressures drive diffusion
O2 pressure is low
Both of these factors cause oxygen to offload