ladybug
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CFTR consist of a single peptide chain with transmebrane segments extra and intracellular regions, whihc of the ff peptide segments of CFTR is most likelt located in a transmembrane segment?
a. Asp-Val-Leu-Thr-Glu-Lys-Glu-Ile
b. Glu-glu-Thr-glu-glu-glu-val-gln
c. ilr-phe-val-leu-ile-tryp-cys-leu
d. lys-ile-lys-his-ser-arg-gly-arg
e. ser-thr-gly-ala-gly-lys-thr-ser
Help me. Kindly explain?
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| robin082006
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????????? no idea
Just guess when having a q like this.
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| Bartek
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I perhaps choose C.
Why?
Most probably part of chain which is inside membrane - in the lipid bilayer - will consist mainly of hydrophobic amino acids. In C - unlike in A, B, D, E - we have only very hydrophobic aminoacids.
reference:
http://www.russell.embl-heidelberg.de/aas/hydroph...
Further:
In labs, if you look for transmembrane part of aa chain you calculate hydrophobicity index (more technics are used but this one is OK). I.e., to determine probability of aminoacid sequence to be found in transmembrane segment you can rate each aminoacid 'hydrophobicity', and this calculation technic is described here:
http://baygenomics.ucsf.edu/education/workshop2/t...
(usualy it is perforemed using computer software, but general rule is: the more hydrophobic aminoacids, the higher probability that it is part of transmembrane chain).
So this question proves that sometimes it is good to remember which aminoacid is hydrophobic (my memo: 'film WC V').
best regards
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| dariush
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thanks for the complete explanation Bartek 
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| guest007
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my answer will be C too....but my funda will be presence of phenylalanine in the amino acid chain...remember in CYstic fibrosis.....F508 what changes,,,,,phenylalanine...so thts the reason i wud have chosen C.....though....hydrophobic amino acids logis is good too...infact combining the two its sure tht the anwser is C.
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| trahuidio
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Can someone please send me the nbme 2 - 4 questions?? It would be a great learning tool for discussion on the forum and in studying for the step.
Thanks,
rluwandam@yahoo.com
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| nadiabarati
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hey we don't have phe in CF gene because of deletion of 3 bases that code for phe. But the rational for hydrophobicity seems nice. So I'm quite confused
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| DrVirgo
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what is (my memo: 'film WC V').??
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| DrVirgo
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According to Kap:
Hydrophobic aa's: Phe, Tyr, Trp, Val, Leu, Ile, and Pro.
Hydrophilic aa's: Ser, Thr, Asp, Cys, and Met
Any mnemonics?? 
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| study_ing
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sis(CYS)ter THRew WATER MElon At SiR
cyst threoninie hydrophillic MEt Asp Ser
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| Omanych
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cysteine is hydrophilic, so C is not entirely hydrophobic!
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