BCH210H1 Lecture Notes - Lecture 16: Conformational Change, Phenylalanine, Schiff Base
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BCH210H1 Full Course Notes
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Problem 1: peptide backbone is highly polar (nh & c=o: solution: the -helix. Problem 2: hydrophobic aa"s generally have low propensity to form alpha- helices. Hydrophobic side chains point out towards the hydrophobic membrane: hydrophilic items are kept within the helix minimize disruptive force. Intra-molecular h-bonds neutralize polar backbone i i+4 traverse membrane w/ minimal disruption: very small & compact always crosses the membrane as alpha helix not other structure! 20-25 residues are required to span the whole lipid bilayer: lipid bilayer is 3-4 nm thick. Most hydrophobic aa"s don"t like to form -helices. Val, ile, phe (generally form beta-sheets, not helices) Backbone neutralization & hydrophobicity main determining factors in aa formation. Aa structural propensities not as important: chou-fasman rules still apply, but there"s always a battle b/w propensity & hydrophobicity. Though chou-fasman determined it wasn"t a great alpha helix former. Allows for extensive van der waals contact: glycophorin a self-associates through glycines.