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
