Protein Function Flashcards
How is oxygen transported around the body?
Oxygen binds to the Haem group on red blood cells
Binds to the Fe2+
How does the Fe bind to the Haem group?
Histidine Residue
What is Myoglobin’s structure?
153 aa
compact
mainly Alpha helix
His 93 in 8th Alpha helix is covalently linked to Fe
What does binding of oxygen do to the Fe in myoglobin?
Moves from slightly below the plane of the ring to in the plane of ring changing the conformational shape
What does oxygen binding to myoglobin show?
A hyperbolic dependence on oxygen concentration
What are the features of haemoglobin structure?
2 polypeptide chains
2 alpha and 2 beta
What does oxygen binding to haemoglobin promote?
Stabilisation of the R state
What is the T state?
Low affinity state
What is the R state?
High affinity state
Why is the oxygen binding curve for haemoglobin sigmoidal?
Due to cooperative binding of oxygen as affinity increases as more oxygen molecules bind to the Hb subunit e.g. 1st O2- low affinity
4th O2- High affinity
What does cooperative binding mean for oxygen transport?
O2 can be efficiently carried from lungs to tissues and more sensitive to small change in O2 concentrations
What is BPG?
2,3- Biophosphoglycerate
What does BPG do?
Decreased the affinity for Oxygen
When does BPG concentration increase?
At high altitudes so O2 is released from tissues
What is the Bohr effect?
Binding of H+ and CO2 lowers the affinity for oxygen
Metabolically active tissues produce lots of H+ and CO2
this ensures delivery of O2 is coupled with demand
Why is CO poisonous?
Combines with Ferromyoglobin and Ferrohaemoglobin and blocks oxygen transport
How much more readily for CO bind to Haemoglobin than O2?
250x
When would CO levels become fatal?
When COHb is more than 50%
What does CO binding to for unaffected subunits?
increase affinity for oxygen
What is the different between Adult and Foetal Haemoglobin?
Adult contains 2 alpha and 2 beta
Foetal contains 2 alpha and 2 gamma
Why is Foetal haemoglobin so important?
Allows transfer of oxygen to Foetus from the mother due to higher affinity
What is the mutation in Sickle Cell anaemia?
Glutamate to Valine in Beta Globin
Why does the Sickle cell mutation cause a problem?
Sticky hydrophobic posted form by the Valine which allow deoxygenated HbS to polymerize causing sickle shape- prone to anaemia and more rigid so cause blockages
What is Thalassaemia?
Inbalance between number of alpha and beta chains
What is a- Thalassaemia?
decreased or absent alpha globin chain
shows before birth
Beta chains can form stable tetramers with increased affinity for oxygen
What is B- Thalassaemia?
Decreased or absent beta globin chains
alpha chains cannot form stable tetramers
shows after birth
What do activators do to the curve?
Shift to left and enhance high affinity R state
What do allosteric inhibitors do to the curve?
Shift to the right and enhance low affinity T state
