Term
| which Hb is in the Tense state? |
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Definition
DeoxyHb
this is known as the T state |
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Term
| which Hb is in the Relaxed state? |
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Definition
OxyHb
on oxygenation the distance between iron atoms in B chains decreases from 3.99 to 3.34nm. |
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Term
| on oxygenation of Hb what happens to the distance between iron atoms on B chains? |
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Definition
| the distance decreases from 3.99 to 3.34 nm |
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Term
| the T state is constrained and stabilised by which two types of bonds? Which terminal basic amino acids of each subunit are involved?? |
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Definition
the Tense state constrained and stabilised by hydrophobic and 8 electrostatic bonds.
this involves the C-terminal basic amino acids of each subunit |
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Term
| what are the C- terminal basic amino acids of each subunit in Hb? |
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Definition
alpha = Tyr and Arg (141)
Beta = Tyr and His (146)
each of the penultimate Tyr is held in a pocket by H-bonding to a Val. this anchors the C-terminal residues in positions favourable for electrostatic bonding. In addition, the binding of 2,3 BPG between B subunits further stabilises the T state. |
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Term
| each penultimate Tyr residue in each unit of Hb is held in a pocket by H-bonding to a Val. what does this do? which other molecule that binds between B subunits further stabilises the T state? |
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Definition
H-bonding of penultimate Tyr to Val anchors C-terminal residues in positions favourable for electrostatic bond formation.
the binding of 2,3 BPG in between B subunits further stabilises T state Hb
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Term
| in deoxyHb which Histidine is bonded to the Fe (II) by how many nm is the Fe(II) above the plane of the porphyrin ring? |
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Definition
the proximal Histidine F8 is bonded to Fe (II) in the deoxyHb state. the Fe(II) is above the plane of the porphyrin ring by 0.06nm (0.6A)
the binding of one o2 molecule to the iron pulls it in 0.039nm closer into the porphyrin plane. |
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Term
in deoxyHb the Proximal His F8 is bound to Fe(II). the Fe(II) is above the plane of the porphyrin ring by 0.06nm (0.6A)
how much is the Fe(II) pulled in closer to the porphyrin ring by the bonding of an o2 molecule with the Fe (II)? |
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Definition
the binding of one o2 molecule to the Fe (II) pulls the Fe(II) closer to the porphyrin ring by 0.039nm
here a tiny change in the position of Fe(II) group causes a very large implication in shape. |
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Term
| as the Fe(ii) moves as a result to o2 binding, it drags the His F8 so that the helix F, the EF corner and the FG corner follow. what happens as a result of this movements? |
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Definition
the movements are transmitted to the subunit interfaces and result in the breaking of the 8 electrostatic bonds.
as a result, a new conformation is fomred |
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Term
the shift in helix F results in a crucial change: the penultimate Tyrosine residues pop out of their H-bonded pocket with valines breaking the elctrostatic bonds that stabilies the T state.
how many degrees are the a1,b1 subunits rotated by with respect to a2,b2 subunits? |
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Definition
a1,b1 subunits rotated by 15 degrees with respect to a2,b2 subunits
thus in the Relxaed state, the 8 electrostatic bonds are broken. In addition, the B subunits are now closer and the site for 2,3 BPG binding is no longer available |
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Term
| the binding of oxygen moves the fe(ii) 0.039nm closer to the porphyrin ring. the fe(ii) drags the proximal His f8 so that the helix F, EF corner and FG corner follow. this causes the penultimate tyr to op out of thier h-bonded pocket with valine in turn breaking the electrostatic bonds. what happens to the distance between the B subunits and the bidnig site for 2,3 BPG? |
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Definition
| the distance between the beta subunits decrease as they move closer so the binding site for 2,3 BPG is no longer availbale. in the R state of Hb the electrostatic bonds are broken. |
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Term
| o2 binds to ....... this pulls the ...... His in the... helix. changes are transmitted to the ............ interfaces. 8 ................... bonds are broken. the .............. site is lost. one AB subunit ......... by ..... degrees with respect to the other |
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Definition
Fe(ii), proximal, F, subunit, electrostatic, 2,3 BPG, rotates, 15
o2 binds to fe(ii). 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 with respect to the other |
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Term
| retinol binding protein RBP is an example of which structural protein? |
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Definition
beta barrel protein.
Retinol is also known as Vitamin A. it is a lipid alcohol, synthethised in the liver and transported to Vit A dependant tissues by a small protein called RBP. Mr 21kDa |
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Term
true or false?
vitamin A is toxic in excess? |
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Definition
| this is true and that is why you shouldnt eat a polar bears liver because it is packed full of vitamin A. |
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Term
| retinol is one of several forms of active vitamin a. what is it derived from? |
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Definition
| derived from Beta carotenes synthethised by plants. it is cleaved to retinol by most animlas and can be stored in the liver as retinol palmitate |
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Term
| retinol can be stored in the liver in which form? |
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Definition
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Term
| how many strands are there in the structure of RBP beta barrel topology? |
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Definition
8 strands
the retinol binding site is lined with hydrophobic residues such as Phe, Met and Tyr |
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Term
| why is the retinol binding site lined with hydrophobic and not polar residues? |
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Definition
| because retinol is a lipid alcohol, a steroid hormone that is hydrophobic thus the requirement for the hydrophobic residues in the lining of the binding site on the RBP |
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Term
when a single molecule of retinol is bound by the RBP, it then binds to a larger molecule. name this molecule
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Definition
| Transthyretin - this stabilises it preventing its loss by the kidney and transports it to the cell-surface receptors which recognise the entire complex. |
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