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Sugars 10/29/09
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Carbohydrate and sugar structure
Carbohydrates or saccharides are essential components of living organisms. (C•H2O)n Where n=3 or greater. A single saccharide is called a monosaccharide. Oligosaccharide is a few linked monosaccharides and are at time associated with proteins (glycoproteins) or lipids (glycolipids) Polysaccharides consist of many monosaccharides i.e. cellulose or glycogen
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Monosaccharides (D-aldoses)
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The Fischer convention, the basis for the D- configuration in sugars comes from D-glyceraldhyde’s configuration around its asymmetric carbon. Note there are 2(n-2) stereoisomers. Epimers differ in configuration around one carbon atom i.e. D-glucose and D-mannose but D-galactose and D-mannose are not epimers as they vary around two carbon atoms.
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Monosaccharides (D-aldoses)
Epimers Not Epimers
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Carbohydrates are classified as to the nature of the carbonyl group : ketone = ketose aldehyde = aldose Triose Tetrose Pentose Hexose 2(n-3) stereoisomers of ketoses c.f. 2(n-2) stereoisomers of aldoses
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Monosaccharides can form ring structures
Note that unlike condensation reactions there is NO loss of a water molecule in these cyclization reactions.
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b-above plane a-below plane
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Glycosidic bonds are between two sugars
They can either be in the a or b configuration and can be linked through the 1-2, 1-4 or 1-6 linkage Note loss of water from condensation reaction above.
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Sugar Polymers The Polysacchrides
Energy Storage Starch a-amylose and amypectin Structural Cellulose and Chitin Glycosaminoglycans Proteoglycans
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a-amylose (starch) / Cellulose (poly b-glucose)
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Glycosaminoglycans & Proteoglycans
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Bacteria Cell Walls
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Peptidoglycan
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Next Lecture Tuesday 11/03/09 Glycolysis I
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