Flashcards in MCGB - Protein Function/Oxygen Transport Deck (21):
What does haem consist of?
A protoporphyrin ring and an Fe atom bound to four N atoms in the ring. Fe2+ makes two additional bonds to oxygen, one on each side.
How is Fe bound to the protein in haemoglobin?
Via a histidine residue (proximal histidine).
How much of the myoglobin molecule is alpha-helical?
When oxygen binds to the Fe in deoxymyoglobin, it causes the Fe to move upwards slightly into the plane of the ring, causing what?
A conformational change
What does Y refer to on an oxygen saturation graph?
Percentage saturation with oxygen
What does P50 or P1/2 (numbers should be subscript) refer to?
Partial pressure giving 50% saturation, similar to Km.
What shape is the oxygen binding graph of myoglobin?
What is the difference between the oxygen dissociation curves for myoglobin and haemoglobin?
Haemoglobin's is shifted to the right slightly, and sigmoidal rather than hyperbolic.
Deoxyhaemoglobin can exist in T state or slightly relaxed R state. Which has the higher affinity?
T is low affinity, R is high affinity. Oxygen binding causes it to go from the T state to the R state.
Why is the oxygen binding curve for haemoglobin sigmoidal?
It is difficult for the first O2 molecule to bind, but it gets easier for each one after that due to the increasing affinity for O2.
How does BPG regulate oxygen binding?
It binds to de-oxygenated RBC, promoting release of remaining O2 when in tissues.
How do H+ and CO2 regulate oxygen binding?
Metabolically active tissues produce large amounts of H+ and CO2 which can bind to haemoglobin, lowering affinity and making it drop remaining O2. This means metabolically active tissues receive more O2.
What does carbon monoxide do to haemoglobin?
It binds 250x more readily than O2, meaning that it will not release from haemoglobin. When COHb is above 50%, it is fatal.
How is HbA changed into HbA1C?
Where is HbF found?
In foetal blood
Does HbF have a high or low affinity for O2?
Higher affinity for O2 than HbA, so O2 transfers over to foetal blood supply.
Sickle cells can cause a "sickle cell crisis". What is this?
Crisis occurs when sickle cells block microvasculature due to being more rigid.
What are thalassaemias?
A group of genetic disorders with an imbalance between the number of alpha and beta globin chains.
Give some characteristics of beta-thalassaemias.
Decreased/absent beta globin chain production
- Alpha chains unable to form stable tetramers
- Symptoms appear after birth
Give some characteristics of alpha-thalassaemias.
- Decreased/absent alpha globin chain production
- Several different levels of severity due to multiple copies of alpha chains
- beta chains can form stable tetramers
- onset before birth