chapter7 RKW

chapter7 RKW - Lecture Connections 7 | Carbohydrates and...

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Lecture Connections 7 | Carbohydrates and Glycobiology © 2009 W. H. Freeman and Company
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CHAPTER 7 Carbohydrates and Glycobiology Structures and names of monosaccharides Open-chain and ring forms of monosaccharides Structures and properties of disaccharides Biological function of polysaccharides Biological function of glycoconjugates Key topics about carbohydrates :
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Carbohydrates Named so because many have formula C n (H 2 O) n Produced from CO 2 and H 2 O via photosynthesis in plants Range from as small as glyceraldehyde (M w = 90 g/mol) to as large as amylopectin (M w = 200,000,000 g/mol) Fulfill a variety of functions including: energy source and energy storage structural component of cell walls and exoskeletons informational molecules in cell-cell signaling Often covalently linked with proteins to form glycoproteins and proteoglycans
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Carbohydrates Comprise most of the food we eat ‘Hydrates’ of carbons, i.e. most follow formula C n (H 2 O) m Fuel molecules, metabolic intermediates and energy storage molecules • ATP, NADH, FADH 2 all have carbohydrate components Can be monomeric or polymeric: e.g. monosaccharides, disaccharides, polysaccharides – 20 or more units.
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Monosaccharides • Simplest carbohydrates--many are (CH 2 O) n Either aldehydes or ketones with 2 or more OH Smallest are n=3 C’s, the trioses Glyceraldehyde (aldotriose) Aldose because of aldehyde group Single asymmetric C, therefore 2 stereoisomers (D and L) Dihydroxyacetone--ketose because of keto group No asymmetric C, ketoses have 1 less assym. C than aldoses Aldoses & ketoses with 4-7 C’s called tetroses, pentoses, hexoses, and heptoses respectively For sugars with >1 asymmetric C, D & L refer to asymmetric C farthest from aldehyde or keto group
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Aldoses and Ketoses An aldose contains an aldehyde functionality A ketose contains a ketone functionality
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Enantiomers Enantiomers: stereoisomers that are non-superimposable mirror images In sugars that contain many chiral centers, only the one that is most distant from the carbonyl carbon is designated as D or L D and L isomers of a sugar are enantiomers e.g. L and D glucose have the same water solubility Most hexoses in living organisms are D stereoisomers Some simple sugars occur in the L-form, such as L- arabinose
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Used for Determining Stereo-center label .
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Diastereomers Diastereomers: stereoisomers that are not mirror images – Multiple chiral centers. Diastereomers have different physical properties e.g . water solubilities of threose and erythrose are different
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Drawing Monosaccharides Chiral compounds can be drawn using perspective formulas However, chiral carbohydrates are usually represented by Fischer projections Horizontal bonds are pointing towards you; vertical bonds are projecting away from you
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Nomenclature Isomers--different compounds having same molecular formula, e.g. ethanol vs. dimethyl ether
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This note was uploaded on 03/08/2012 for the course CHEM 481 taught by Professor Wood during the Fall '10 term at BYU.

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chapter7 RKW - Lecture Connections 7 | Carbohydrates and...

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