Haemoglobin Flashcards
What is haemoglobin?
A large protein with a quaternary structure: it is 4 polypeptide chains and 4 iron ion prosthetic groups which travels in blood to carry oxygen
Structure of haemoglobin
4 polypeptide chains
2 alpha glob in 2 beta globin
4 iron haem groups
Where does oxygen bind to in haemoglobin?
4 iron prosthetic groups
Loading and unloading of oxygen to haemoglobin
Haemoglobin + 4 oxygen to form oxy haemoglobin
A reversible reaction so oxy haemoglobin can unload all 4 oxygen
Loading
Oxygen binds to iron in haemoglobin
Unloading
Oxygen unbinds from oxyhaemoglobin
What does the loading of oxygen onto haemoglobin depend upon?
The affinity haemoglobin has for oxygen
What affects the affinity haemoglobin has to oxygen?
The partial pressure of oxygen in the area
Trend for oxygen loading onto haemoglobin
Where there is a high partial pressure for oxygen, oxygen will unload onto haemoglobin more so higher affinity
So haemoglobin has a high % saturation to oxygen
Where does oxygen mostly load onto haemoglobin?
In the alveoli in the lungs because a high partial pressure of oxygen
Oxygen diffuses into blood from alveoli into blood
Trend for oxygen unloading from haemoglobin
Where there is a low partial pressure for oxygen, oxygen will unload from haemoglobin
So less affinity
And lower % saturation of haemoglobin with oxygen
Where does oxygen unload from haemoglobin?
In respiring tissues where oxygen has been used in respiration so has a low partial pressure of oxygen into cells
Affinity for oxygen in lungs
High
Affinity for oxygen in respiring tissues
Low
Partial pressure of oxygen
A measure of oxygen concentration in a given volume caused by oxygen molecules colliding which exerts pressure
Dissociation curve
Shows the % saturation of haemoglobin with oxygen on y axis
Partial pressure of oxygen on x axis
Thus overall affinity oxygen has to haemoglobin at various pO2
Shape of a dissociation curve
S shaped
Why is the dissociation curve or haemoglobin not linear but S shaped?
Due to the structure of haemoglobin and the 4 binding sites of oxygen: as more oxygen binds, tithe affinity for oxygen decreases
Steep S shaped part of dissociation curve ?
When 1 oxygen binds to a haem group, the shape of haemoglobin (tertiary structure) alters to make it easier for more O2 to bind thus for a small increase in pO2, the % saturation increases rapidly
Bohr effect
The partial pressure of CO2 in a cell can affect the unloading of oxygen
Effect of increasing pCO2
Haemoglobin unloads easily
So at a given partial pressure of oxygen, there is a lower % saturation of haemoglobin with oxygen
Effect of increasing pCO2 on the graph
Shifts right
Effect of decreasing pCO2
There is higher affinity for oxygen so oxygen doesn’t unload from haemoglobin easily
Effect of decreasing pCO2 on the graph
Shifts left so for any given pO2, the % saturation haemoglobin has of oxygen is higher (so lower affinity)
What factors can affect the type of haemoglobin in an organism (thus affinity for O2)
Oxygen level in environments
Activity levels
Size
Animals which live in environments with low oxygen levels?
Haemoglobin has high affinity for oxygen compared to living in normal pO2 environments
So it can bind to any available oxygen so high % saturation for a given pO2
Effect on the graph of living in low pO2 environments
Shifts left so for a given partial pressure, higher affinity for oxygen for given pO2
Animals with high activity levels?
Have high activity have a higher demand for oxygen thus need a lower affinity for oxygen at a given pO2 so more oxygen unloaded to respiring tissues
Effect on the graph of animals with high activity levels
Shifts right for a given partial pressure, the % saturation of oxygen is lower
Animals that are smaller effect?
Higher sa:vol ratio so lose heat easily
More metabolic rate to maintain body temp so higher demands for O2
So for a given pO2, the affinity to oxygen is lower
