One method for separating polypeptides makes use of their different solubilities

Question

One method for separating polypeptides makes use of their different solubilities. The solubility of large polypeptides in water depends upon the relative polarity of their R groups, particularly on the number of ionized groups: the more ionized groups there are, the more soluble the polypeptide Which of each pair of the polypeptides that follow is more soluble at the indicated pH? (a) (Gly)20 or (Lys-Ala) at pH 7.0 O (Lys-Ala)3 O (Gly)20 (Glu)20 or(Phe-Met)3 at pH 7.0 O Phe-Met O (Glu)20 (c) (Ala-Asp-Gly)5 or (Asn-Ser-His)5 at pH 3.0: O (Asn-Ser-His)5 O (Ala-Asp-Gly)5 (d) (Ala-Ser-Gly)5 or (Asn-Ser-His)5 at pH 6.0: O (Asn-Ser-His)5 O (Ala-Ser-Gly)5

Explanation / Answer

polypeptide which contains polar or charged side chains are mole soluble than nonpolar side chains

A. (gly)20 is uncharged at ph 7.0 . (lys-Ala)3 is positively charged at ph 7, and its more soluble

B. (glu)20 is negitive charges ta ph 7.0, and (phe-met)3 is less polar and less soluble,( glu)20 is more soluble

C.the carboxilate group of Asp reduces are neutral and partially protonated, imadazole groups of His reduces are positively charged and completely protonated.(Asn-Ser-His) is more soluble

D.In (Asn-ser-his)5, the side chains are polar and His side chains are partially protonated at pH 6.0

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