lecture 20 - MCB 354 Lecture 20 Monosaccharides Reading in...

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Unformatted text preview: MCB 354 Lecture 20 Monosaccharides Reading in Lehninger : Chapter 7 , pp. 235-241 Carbohydrates Most abundant biomolecules on Earth Oxidation of carbohydrates is central energy-yielding pathway in most non-photosynthetic cells Carbohydrate polymers. structural (in plants , insects , bacteria , fungi ) storage (starch, glycogen) protective (lubrication of joints) cell-cell recognition and adhesion 20-1 Classes of saccharides Monosaccharides = single polyhydroxy aldehyde or ketone unit, cyclized , (e.g. 6-carbon glucose, most abundant in nature) Oligosaccharides = short chain of 2- ~20 monosaccharides joined by glycosidic bonds (eg. disaccharide sucrose = glucose-fructose) oligosaccharides > 3 residues are usually joined to protein or lipid in glycoconjugates Polysaccharides chains > ~ 20 to 1000s of monosaccharides in length linear : eg. cellulose (glucose)n branched : eg. glycogen & starch (glucose) depending on the sugar residues in a polysaccharide and the linkages between them, polysaccharides can have very different biological roles 20-2 Have unbranched carbon chains in which all C atoms are linked by single bonds In the linear (open chain) form, one of the C s is double-bonded to O (= carbonyl), and each of the other C s has an - OH : H2O-soluble If the C=O is at:- the end of a carbon chain (i.e. in an aldehyde), monosaccharide = aldose- at any other position (i.e. in a ketone group), monosaccharide = ketose Monosaccharides-1 Simplest monosaccharides have 3 carbons......
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lecture 20 - MCB 354 Lecture 20 Monosaccharides Reading in...

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