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Unformatted text preview: Question: Which of these arrangements of proteins have been found in biological membranes? Answer: A, B, D, E, F, I C: carbohydrate on cytoplasmic side never found G: protein completely buried never found, theoretically unlikely H: tip only in membrane never found, unlikely Bonus Question (not used in class): Question: Why are membrane-spanning protein segments almost always alpha-helices or beta-barrels, but never disordered chains? Answer: In both alpha- helix and beta-barrel, the polar H-bonding groups in the peptide bond make internal hydrogen bonds with other peptide bonds. In a disordered chain the peptide polar groups are not bonded to each other or to lipid. As a result, a disordered peptide chain in a membrane is energetically very unfavorable....
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- Winter '10