3. Protein Function Flashcards
Why does oxygen need haemoglobin to transport it around the body?
Because it isn’t polar so can’t dissolve in the blood and therefore needs a pen effective solution for being transported around the body.
What part of the haemoglobin molecule does oxygen bind to?
The Fe2+ part of the haem group.
How many oxygen molecules can bind to a haemoglobin molecule?
2.
List four key feature of myoglobin structure.
It is 153 amino acids long, it is compact, 75% a-helical, His 93 in the 8th a-helix is covalently linked to Fe.
How does oxygen binding affect the shape of myoglobin?
Before binding, the Fe in deoxymyoglobin is below the plane of the ring but when it binds, the Fe moves into the plane of the ring. This affects overall protein conformation.
What are the two curves the myoglobin and haemoglobin have for oxygen dissociation?
Myoglobin has a hyperbolic curve and haemoglobin has a sigmoidal curve.
How do the polypeptide chains of haemoglobin arrange themselves? (Specify what polypeptide chains make up a haemoglobin molecule).
They form a tetramer, made of two a-chains and two B-chains.
What are the relative affinities for oxygen of the T and R state haemoglobin?
T state has a low affinity, but R state has a high affinity for oxygen binding.
What happens to the affinity for oxygen of haemoglobin as more oxygen binds?
Affinity increases.
Which enzyme regulates oxygen binding and what would the affect be if it wasn’t there?
2,3-Bisphosphoglycerate (2,3-BPG). Without it haemoglobin would show more myoglobin like affinity for oxygen.
Which direction does 2,3-Biphosphoglycerate shift the oxygen affinity curve of haemoglobin and what is the effect?
It shifts it right which lowers the affinity.
How is 2,3-biphosphoglycerate useful in delivering oxygen to tissues and picking it up from the lungs?
It means haemoglobin has a low affinity for oxygen when it is in the tissues so it lets go of the oxygen had delivers it to the tissues. But it has a high affinity for oxygen in the lungs, where there is high oxygen saturation, so picks up oxygen readily.
What is the purpose of increasing 2,3-biphosphoglycerate concentrations at high altitudes?
It means affinity is lowered further so oxygen is readily delivered to the tissues.
What is the Bohr effect?
When H+ and CO2 bind to haemoglobin and lower its affinity for oxygen. It shifts the sigmoidal curve to the right.
What is the purpose of the Bohr effect?
It measures the pH, so as it lowers more oxygen is released. This means the delivery of oxygen is matched to the demand as metabolically active tissues release lots of H+ and CO2.
Why is carbon monoxide poisoning such a problem?
Because carbon monoxide binds to haemoglobin 250x more readily than oxygen.
What defence reaction tries to reduce carbon monoxide poisoning? What is the negative effect of this?
Carbon monoxide binding increases the haemoglobin’s affinity for oxygen so it binds to oxygen more favourably than before. But this means oxygen isn’t delivered to the tissues as easily.
When does carbon monoxide poisoning become fatal?
When COHb>50%.
How can serious cases of carbon monoxide poisoning be treated?
By using blood transfusions.
Why do foetuses have a different kind of haemoglobin (HbF)?
HbF has a higher affinity for oxygen than normal adult haemoglobin, HbA. This means transfer of oxygen from the mother to foetus can happen.
What causes sickle cell anaemia?
A mutation of glutamate to valine in B-globin.
Why is the mutation of glutamate to valine in B-globin a problem?
It causes a sticky hydrophobic pocket to form so HbS (sickle felled anaemia haemoglobin) polymerises and sticks together so the red blood cells can’t pass through micro vascular systems.
What are thalassaemias?
A group of genetic disorder where there is an imbalance between the number of a and B globin chains.
What is the cause of B-thalassaemia and why is this a problem?
There are decreased or absent amounts of B-globin chains produced. The remaining a-globin chains can’t form stable tetramers.
What is the cause of a-thalassaemia and why is this a problem?
There are decreased or absent amounts of a-globin chains produced. The remaining B-globin chains form stable tetramers with increased affinity but less oxygen is delivered to the tissues due to this high affinity.
