BIOL115 - Lecture 5

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  • Created by: Katherine
  • Created on: 13-05-16 09:50
On oxygenation, the distance between iron atoms in b chains changes, how?
The distance decreases from 3.00 to 3.34nm.
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Is Deoxyhaemoglobin in the tense or relaxed state?
It is in the tense state
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Is Oxygaemoglobin in the tense or relaxed state?
It is in the relaxed state.
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The T state is constrained and stabilised by what?
Hydrophobic bons and 8 electrostatic bonds which keeps the haemoglobin together.
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Each of the penultimate Tyr residues is held in a pocket by..
H bonding to a val. This anchors the C terminal residues in positions favourable for electrostatic bond formation.
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In deoxyaemoglobin, the proximal His F8 is bonded to the iron, but where is the Feii?
It is above the plane of the porphyrin ring by 0.06nm.
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The binding of one O2 molecules to iron pulls it how much closer to the porphyrin plane?
0.039nm
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What happens as the iron moves closer to the plane?
It drags the His F8, so that the helix F, the EF coner and the FG corner follow.
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Where are these movements transmitted to, and what results from it?
They are transmitted to the subunit interfaces and result in the breaking of the 8 electrostatic bonds.
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What does the shift in helix F result in?
It results in a crucial change in that the penultimate tryosine residues pop out of their H bonded pocket with valines, breaking the electrostatic bonds the stabilise the T state.
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What is the movement that occurs when there is a shift?
The a1b1 subunits rotate by 15 degrees with respect to the a2b2 ones.
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In the relaxed state, what is the state of the electrostatic bonds and the B subunits?
The electrostatic bonds are now broken. Also the B subunits are now closer and the site for 2,3- BPG binding is no longer available.
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Summary of the main changes:
Oxygen binds to Fe2, this pulls the proximal His in the F helix,, changes are transmitted to the subunit interfaces, 8 electrostatic bonds are broken, the 2,3 bpg site is lost. One ab subunit rotates by 15 degrees.
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What is retinol?
Vitamin A - it is a lipid alcohol, synthesised in the liver, and transported to Vit A dependent tissues by a small protein called retinol binding protein.
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What is retinol derived from?
B carotenes synthesised in plants. It is cleaved to retinol by most animals and can be stored in the liver as retinol palmitate.
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Vitamin A is important as:
An antioxidant, a steroid hormone, a vital component of night vision.
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RBP is an example of ..
B domain protein. It is an up and down B barrel with 8 strands in a simple topology.
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The retinol binding site is lined with hydrophobic residues such as:
Phe, Met, Tyr
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How many molecules of retinol are bound by RBP?
1, and this itself binds to a larger molecules.
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What is the name of the larger molecule, and what does the binding to this do?
Transthyretin - it stabilises it, preventing its loss by the kidney and transports it to cell surface receptors which recognise the entire complex.
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Card 2

Front

Is Deoxyhaemoglobin in the tense or relaxed state?

Back

It is in the tense state

Card 3

Front

Is Oxygaemoglobin in the tense or relaxed state?

Back

Preview of the front of card 3

Card 4

Front

The T state is constrained and stabilised by what?

Back

Preview of the front of card 4

Card 5

Front

Each of the penultimate Tyr residues is held in a pocket by..

Back

Preview of the front of card 5
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