Role of Haemoglobin (Hb) Flashcards
What is the main role of haemoglobin?
Carries oxygen and carbon dioxide around the body
What type of molecule is haemoglobin?
A protein
What does each molecule of haemoglobin contain?
4 haem groups, each able to bond with one molecule of oxygen
What does this contents in haemoglobin therefore mean?
That each molecule of haemoglobin can carry four oxygen molecules or eight oxygen atoms
What is formed when haemoglobin is saturated with oxygen?
(O2 binds to Hb)
Oxyhaemoglobin
What is the equation for this formation?
Oxygen + Haemoglobin ⇌ Oxyhaemoglobin
What does the binding of the first O2 molecule result in?
A conformational change in structure of haemoglobin molecule
What does this conformational change mean?
It makes it easier for each successive oxygen molecule to bind (cooperative binding)
When does the reverse of this happen?
When oxygen dissociates in tissues
What are the 3 factors which determine the affinity of haemoglobin for oxygen?
-pO2
-pCO2
-Type of Hb (fetal or adult)
What does ‘p’ stand for in pO2 and pCO2?
Partial Pressure
What happens as pO2 increases?
Haemoglobin’s affinity for O2 increases.
What does affinity mean?
the strength by which two (or more) molecules interact or bind.
What does it mean if the affinity has a low value?
The smaller its value, the greater the affinity between two molecules and vice-versa
Why is the dissociation curve s-shaped? Start at top and go to bottom
-At top, it’s hard for 4th O2 to bind to as Hb becomes saturated with O2 so it’s shape changes making it difficult for other O2’s to bind
-In middle, easier for 2nd and 3rd O2’s to bind as when 1st O2 binds, it causes Hb’s shape to change making it easier for other O2’s to bind
-At bottom, it’s hard for 1st O2 to bind
What type of saturation is at the bottom of the dissociation curve?
Low as haemoglobin isn’t carrying much O2
-few haem groups bound to O2
What type of saturation is at the middle of the dissociation curve?
Medium as it’s easier for O2 to be picked up
-more haem groups to bound to O2
What type of saturation is at the top of the dissociation curve?
High as all of haemoglobin as all haem groups are bound
What happens are pCO2 increases?
Haemoglobin’s affinity for O2 decreases causing haemoglobin to unload its O2(right where it’s needed) creating the Bohr effect
What is the Bohr effect?
Where haemoglobin dissociation curve moves to right as haemoglobin gives up its O2 more readily when pCO2 is high
Why is the Bohr effect important in the body?
-In active tissues with high partial pressure of CO2, haemoglobin gives up oxygen more readily
-In lungs where the proportion of CO2 in air is relatively low, oxygen binds to haemoglobin molecules easily
What is the pO2 and pCO2 like in lungs?
pO2 is high and pCO2 is low
What is the pO2 and pCO2 like in respiring tissues?
pO2 is low and pCO2 is high
Bohr Effect is result of increased acidity due to dissolved CO2. What 2 things do hydrogen ions do?
-Lower pH
-Reduce affinity of Hb for O2
How is CO2 transported?
Is carried from tissues 3 ways
What are the 3 ways in which CO2 is transported?
-In solution in blood plasma
-In combination with haemoglobin
-As hydrogen carbonate ions in blood plasma
How much of CO2 is transported in solution in blood plasma?
5%
How much of CO2 is transported in combination with haemoglobin?
10%
How much of CO2 is transported as hydrogen carbonate ions in blood plasma?
Most-80%
How is CO2 transported in combination with Hb?
-Amino Acid group on Hb and CO2 in plasma enters into cell and adds to AA group
-This forms carbaminohaemoglobin
How is CO2 transported as hydrogen carbonate ions in blood plasma?
It’s converted into hydrogen carbonate ions (HCO3-) in the cytoplasm of red blood cells
How is Haemoglobinic Acid formed?
Hydrogen ions produced from dissociation of Carbaminohaemoglobin and hydrogen carbonate ions bind to Hb
What does this formation of Haemoglobinic Acid cause?
Causes Hb to release its oxygen
In what forms does haemoglobin exist in?
Adult and Foetal
What other form of haemoglobin is there which is less common?
Myoglobin which is found in muscles of vertebrates
What is the role of Myoglobin?
Concerned with storage rather than transport of oxygen
-is like a last resort
Why is foetal and adult haemoglobin different?
If mother and foetus had the same Hb, there would be no reason for oxygen to pass from one to another (starvation of oxygen would occur)
Where are foetal RBCs produced?
In liver
Where does this production happen after birth?
In bone marrow with adult Hb
Why does foetal Hb have a higher affinity for O2 than adult?
As it’s made from 2 alpha and 2 beta polypeptide chains
What are the 2 reasons why it is important that foetal Hb has a higher affinity?
-pO2 at placenta is lower than at lungs as some O2 is used up en-route by mothers body
-we need foetal Hb to load O2 while mother Hb unloads O2
What happens to the dissociation for foetal Hb?
Shift to left
