(Please note that this is the same material but with different questions...) The
ID: 7702 • Letter: #
Question
(Please note that this is the same material but with different questions...)The extent of branching (number of a1?6 glycosidic bonds) in amylopectin can be determined by extensive methylation followed by identification of the hydrolysis products of the methylated polysaccharide, as follows: A sample of amylopectin is exhaustively treated with a methylating agent (methyl iodide) that replaces all the hydrogens of the sugar hydroxyls with methyl groups, converting –
OH to –OCH3, an ether functional group. All the glycosidic bonds in the methylated sample are then hydrolyzed in aqueous acid, and the various methylated derivatives are quantitated.
What derivatives you would expect of the monosaccharides that were
C. from the a(1?6) branch points in the molecule?
D. involved only in internal a(1?4) linkages?
Explanation / Answer
Both a(1-->6) branch points and internal a(1-->4) linkages are protected from linkage as they are involved in glycosidic linkages. During complete methylation and subsequent hydrolysis, the branch point residues yield 2,3-Di-O-methyl glucose and unbranched residues yield 2,3,6,-tri-O-methyl glucose.
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