lecture 21 - MCB 354 Lecture 21 Glycosidic Linkages...

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MCB 354 Lecture 21 Glycosidic Linkages Polysaccharides Reading in Lehninger : Chapter 7 , pp. 241-252
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21-1 Reducing sugars The anomeric carbon of Glc and other sugars can be oxidized by mild oxidizing agents such as Cu2+ , providing the sugar is in its open chain form, with a “free” carbonyl carbon at C-1 Sugars capable of reducing Cu2+ are called “reducing sugars” The end of a chain of sugars that has a free anomeric (C-1) carbon is called the reducing end RED COLOR
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Reaction = formation of an acetal from a hemiacetal (e.g. C-1 of gluco- pyranose) and an alcohol (-OH group on C-4 of second glucopyranose molecule) O -glycosidic bonds are formed when the -OH group of one sugar reacts with the anomeric carbon another Joining of sugars via glycosidic bonds 21-2 ANOMERIC CARBON
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When an anomeric carbon participates in a glycosidic bond, it cannot exist in linear form, and can no longer act as a reducing sugar (can’t reduce Cu2+) The end of a di- or polysaccharide chain with a free anomeric carbon (ie. not involved in a glycosidic bond) = the “reducing end” In maltose, the configuration of the anomeric carbon in the glycosidic linkage is α Glycosidic bonds are readily hydrolyzed by mild acid α OR β b/c MUTAROTATION α NON- REDUCING END REDUCING END α OR β b/c MUTAROTATION α Joining of sugars via glycosidic bonds 21-3
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NON-REDUCING: BOTH ANOMERIC CARBONS PARTICIPATE IN GLYCOSIDIC BOND Disaccharides 21-4
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Naming of di- and oligosaccharides Name describes compound w. its non-reducing end to the left, and is “built up” in the following order: Give config. at anomeric carbon joining 1st monosacch. unit (on left) to the second Give name of non-reducing residue, inserting “ furano ” or “ pyrano ” to distinguish 5- and 6-membered rings Give the numbers of the 2 carbon atoms joined by the glycosidic bond
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This note was uploaded on 01/29/2012 for the course MCB 354 taught by Professor Spees during the Spring '09 term at University of Illinois, Urbana Champaign.

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lecture 21 - MCB 354 Lecture 21 Glycosidic Linkages...

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