Protein Function - Oxygen Transport Flashcards
Why does oxygen need a transport molecule in the body?
It is non-polar and can’t be dissolved
What is the structure of a haem group?
An Fe atom bound to 4N atoms of the ring
How is the Fe atom bound to the protein?
Via a histidine residue
What is the general structure of myoglobin?
- Tertiary
- Single sub unit
- Alpha helices only
What shape of curve is represented by myoglobin on a graph of oxygen concentration?
Hyperbolic curve
Describe the general structure of haemoglobin
- 2 alpha and 2 beta chains in a tetramer
- Four subunits each with a haem group
- Structural change when it binds to oxygen
What are the two states of haemoglobin and what do they indicate?
T-State - Compact with low oxygen affinity
R-State - Open structure with high oxygen affinity
What does oxygen binding to haemoglobin promote?
Stabilisation of the R-State
How does haemoglobin demonstrate cooperative binding?
The oxygen binding affinity increases as more oxygen binds to the subunits
How does affinity affect binding of oxygen to haemoglobin?
- First oxygen molecule to first subunit is hard due to low oxygen affinity
- Last oxygen molecule to last subunit is easy due to high affinity
How is the sigmoidal curve of haemoglobin beneficial?
- Oxygen can be efficiently carried from the lungs to the tissues
- More sensitive to small differences in oxygen concentration
- Allows for efficient oxygen binding and delivery
Name 2 allosteric effectors of haemoglobin
- 2,3-Bisohosphoglycerate (BPG)
- CO2 and H+
Define an allosteric activator of haemoglobin
Shifts curve to the left and enhances the high affinity R-state
Define an allosteric inhibitor of haemoglobin
Shifts curve to the right and enhances the low affinity T-state
What is the effect of BPG on haemoglobin?
- It binds to the beta subunit and stabilises the low affinity form
- Shifts curve to the right
- Increases the amount of oxygen to the lungs
What is the effect of CO2 and H+ binding to haemoglobin? What name is given to this?
Bohr Effect - ensures delivery of O2 is coupled to demand
- Lowers oxygen affinity
What effect does carbon monoxide have when it binds to haemoglobin?
It binds more readily than oxygen and blocks oxygen transport
How can carbon monoxide poisoning be treated?
- Increase the partial pressure of oxygen
- Hyperbaric chamber
What are the 3 types of adult haemoglobin?
- HbA
- HbF
- HbA2
Which form of haemoglobin is prevalent in a foetus and why?
- HbF
- HbF has a higher affinity for oxygen than HbA which allows oxygen transfer from mother to baby
What mutation occurs in sickle cell anaemia?
Glutamate is replaced by Valine
What structural change occurs in people with sickle cell disease?
- Hydrophobic pocket formed by valine
- Bigger, sticky complexes formed
- Cells are more rigid and prone to lyse
