Sugars 102909

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Sugars10/29/09
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Carbohydrate and sugar structure
Carbohydrates or saccharides are essential
components of living organisms. (CH2O)n Where
n3 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-glyceraldhydes 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 LectureTuesday 11/03/09 Glycolysis I