Carbonhydrate structure - 1 Carbohydrates most abundant...

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1 1 Carbohydrates • most abundant biomolecules on earth • polyhydroxy aldehydes or ketones • general formula (CH 2 O) 2 e.g. C 6 H 12 O 6 • “carbon and water” • soluble or insoluble • -saccharide sakkharon : meaning sugar in Greek 2 3 major size classes – Monosaccharides • simple sugar, most abundant monsaccharide = D-glucose – Oligosacchararides • short chains of Monosaccharides joined together, most abundant oligosaccharide = disaccharide (e.g. sucrose, or cane sugar = glucose + fructose) – Polysaccharides • long chains of monosaccharides (hundreds to thousands) • linear (e.g. cellulose) or branched (e.g. glycogen) • most abundant polysaccharide: starch and cellulose (consist of long chains of glucose) 3 Monosaccharides • Monosaccharides are either aldehydes or ketones • Most of them have a sweet taste • 2 forms, either – aldose • carbonyl group at the end of the carbon chain – ketose • carbonyl group at any other position • either aldose or ketose can have any number of carbon atoms: – Tetrose (4C), Pentose (5C), Hexose (6C), Heptose (7C) 4 Asymmetry (or chirality) • cannot superimpose on its image • chiral center is the the carbon atom that has 4 different groups attached to it • D-isomer or L-isomer – D- and L- isomers are mirror images of each other – naturally occurring: D-glucose 5 Asymmetry (or chirality) Fisher projection formula – used to represent 3-dimensional structures
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2 – arrow heads are pointing towards you (out of the paper) – imagine a friend greeting you with the hands opened widely D isomer: – OH group of second last carbon is at the right hand side of the Fisher projection 6 Cyclic forms of monosacch. • Straight chain forms – for representation purposes only • Cyclic forms – most monosacch. are in cyclic forms in solution – straight form <=> cyclic (or ring) form – formed when a carbonyl group forms a covalent bond with oxygen of OH group along the chain. • e.g. carbonyl group at C1 and OH group of C5 in D-glucose, forming D- glucopyranose (pyranose: 6-member ring) 7 Anomers • during ring closure, 2 anomers formed α : OH group of C1 is downward; β : upward α -D-glucopyranose and β -D-glucopyranose • anomers are interchangeable, only in solution form (when the ring opens) α <=> linear form <=> β • anomers are stereoisomers that differ from each other only at one
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Carbonhydrate structure - 1 Carbohydrates most abundant...

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