Lecture 5 Flashcards
(25 cards)
How far away are the iron atoms on the β-chains when deoxygenated?
3.99nm.
How far away are the iron atoms on the β-chains when oxygenated?
3.34nm.
Does the distance between iron atoms on β-chains reduce or increase when oxygenated?
Reduce.
Which word describes the state of deoxyhaemoglobin: T(ense), or R(elaxed)?
Tense.
Which word describes the state of oxyhaemoglobin: T(ense), or R(elaxed)?
Relaxed.
What acts to stabilise and constrain the T state?
Hydrophobic bonds and 8 electrostatic bonds from C-terminal basic AAs of each subunit.
Also binding of 2,3-BPG helps stabilise.
What residue is located at the C-terminal for the α-chains.
Arg(inine).
What residue is located at the C-terminal for the β-chains.
His(tidine).
What is the penultimate residue for both α and β chains?
Also, what are they bonded to, and why?
Tyr(osine).
H-bonded to Val, anchoring C-terminal in position that favours electrostatic bond formation.
In deoxyhaemoglobin, how far is Fe(II) above the plane of the porphyrin ring by?
0.6Å.
When one O2 is bound to the Fe(II), how much closer is it pulled to the porphyrin plane?
0.39Å.
What happens to the haemoglobin’s conformation when the iron moves as it binds with oxygen?
What effect does this have on the 8 electrostatic bonds?
Drags His F8, causing helix F, corner EF and corner FG to follow. These movements transmitted to subunit interface, causing breaking of 8 electrostatic bonds.
When the iron in the haem group of the haemoglobin binds to oxygen, what effect does it have on the relative position of the α1β1 units with respect to the α2β2 units?
The α1β1 units rotate 15º w.r.t. the α2β2 units.
The β subunits move closer together when haemoglobin is oxygenated. What implications does this have?
There is no longer an applicable binding site for 2,3-BPG.
What is an alternative name for retinol?
Vitamin A.
What type of molecule is vitamin A?
A lipid alcohol.
Where is retinol synthesised, and what is it transported to vitamin-A dependent tissues by?
The liver.
Transported by retinol-binding protein (RBP).
What is the Mr of retinol-binding protein?
21,000.
Is retinol the only active form of vitamin A?
No.
What is retinol derived from?
β-carotenes synthesised by plants.
Where is retinol stored, and as what?
Stored in liver as retinol palminate.
3 reasons vitamin A is important?
Anti-oxidant.
Steroid hormone.
Vital component of night vision.
What type (regarding domains) of protein is retinol-binding protein (RBP)?
β-domain.
What type of residues is the retinol binding site lined with? (and 3 examples)?
Hydrophobic residues.
E.g. Phe, Met, Tyr.
