3. Haemoglobin Flashcards
Haemoglobin structure
- Quaternary: 4 polypeptide chains
- Prosthetic group = Haem group
- Each haem group can bind to 1 oxygen molecule
- Globular: soluble in water
Function of haemoglobin
To carry oxygen through the blood from lungs to respiring tissues
How does the structure of haemoglobin relate to its function?
- 4 haem groups: 4 oxygen molecules per haemoglobin molecule so more efficient transport of O2 throughout the body
- Haemoglobin needs to be soluble so that it can be carried in the cytoplasm of the RBCs (the fact that it’s globular means it’s water-soluble)
What is affinity?
How likely haemoglobin is to bind to oxygen
What affects haemoglobin’s affinity for oxygen?
O2 & CO2 levels
The condition affects affinity, NOT LOCATION!
Association is a consequence of high O2 concentration, dissociation is a consequence of low O2 concentration
Haemoglobin + oxygen =
Oxyhaemoglobin
Where does association/loading occur?
In tissues with high oxygen content (i.e. lungs)
Where does dissociation/unloading occur?
In tissues with low oxygen content (i.e. respiring tissues)
X and y axes in an oxygen dissociation curve
X: partial pressure of oxygen (kPa)
Y: % saturation of haemoglobin with oxygen
Explain why oxygen dissocation graphs are S shaped
- Shape of haemoglobin molecule makes it difficult for the 1st O2 molecule to bind: curve is shallow at low oxygen PP
- Once 1st O2 binds the quaternary structure changes: easier for 2nd and 3rd O2 to bind. Small changes in oxygen PP lead to larger changes in % saturation: positive cooperation
- After 3rd O2 binds it’s harder for last to bind because collisions between O2 molecules and final binding site are less likely: curve becomes shallow again
Explain CO2’s effect on haemoglobin
- CO2 lowers pH (acidic when dissolved in blood plasma)
- Lower pH affects tertiary structure (H bonds) of haemoglobin
- Harder for O2 to bind to the haemoglobin
Curve shifts to the left: increased or decreased affinity?
Increased
Curve shifts to the right: increased or decreased affinity?
Decreased
Lugworm: shifts left or right?
Left
Mouse: shifts left or right?
Right
Llama: shifts left or right?
Left
Foetus: shifts left or right?
Left
Myoglobin is found in muscles. It acts as an oxygen store, only releasing its oxygen if the oxygen levels in the muscle drop really low. Would myoglobin have a higher or lower affinity for oxygen than haemoglobin?
Higher
Curve shifts to the left
