CARBOHYDRATES 2: Oligosaccharides

CARBOHYDRATES 2: Oligosaccharides

Oligosaccharides: disaccharidesMost common are the disaccharidesSucrose, lactose, and maltoseMaltose hydrolyzes to 2 molecules of D-glucoseLactose hydrolyzes to a molecule of glucose and a molecule of galactoseSucrose hydrolyzes to a moledule of glucose and a molecule of fructose

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Cellobiose, a product of cellulose breakdown, is the otherwise equivalent b anomer (O on C1 points up). The b(1 4) glycosidic linkage is represented as a zig-zag, but one glucose is actually flipped over relative to the other.

Disaccharides:Maltose, a cleavage product of starch (e.g., amylose), is a disaccharide with an a(1 4) glycosidic link between C1 - C4 OH of 2 glucoses. It is the a anomer (C1 O points down).

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Other disaccharides include: Sucrose, common table sugar, has a glycosidic bond linking the anomeric hydroxyls of glucose & fructose. Because the configuration at the anomeric C of glucose is a (O points down from ring), the linkage is a(12). The full name of sucrose is a-D-glucopyranosyl-(12)-b-D-fructopyranose.)Lactose, milk sugar, is composed of galactose & glucose, with b(14) linkage from the anomeric OH of galactose. Its full name is b-D-galactopyranosyl-(1 4)-a-D-glucopyranose

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Sucrosea-D-glucopyranosido-b-D-fructofuranosideb-D-fructofuranosido-a-D-glucopyranosidealso known as tablet sugarcommercially obtained from sugar cane or sugar beethydrolysis yield glucose and fructose (invert sugar) ( sucrose: +66.5o ; glucose +52.5o; fructose 92o)used pharmaceutically to make syrups, troches

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Sugar caneSugar beet

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Lactoseb-D-galactose joined to a-D-glucose via b (1,4) linkagemilk contains the a and b-anomers in a 2:3 ratiob-lactose is sweeter and more soluble than ordinary a- lactoseused in infant formulations, medium for penicillin production and as a diluent in pharmaceuticals

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Maltose2-glucose molecules joined via a(1,4) linkage; bent structureknown as malt sugarproduced by the partial hydrolysis of starch (either salivary amylase or pancreatic amylase)used as a nutrient (malt extract; Hordeum vulgare); as a sweetener and as a fermentative reagent

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Cellobiose2-glucose molecules joined via (1,4) linkageHydrolysis product of cellulose on cellulosic materialsHas linear structure

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Other Oligosaccharides

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Honey also contains glucose and fructose along withsome volatile oils

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starchStructures of some oligosaccharides

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Structures of some oligosaccharides

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Structures of some oligosaccharidesAn enzymatic product (Beano) can be used to preventthe flatulence

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Oligosaccharides occur widely as components of antibiotics derived from various sources

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Polysaccharides or glycanshomoglycans (starch, cellulose, glycogen, inulin)heteroglycans (gums, mucopolysaccharides)characteristics:polymers (MW from 200,000)White and amorphous products (glassy)not sweetnot reducing; do not give the typical aldose or ketose reactions)form colloidal solutions or suspensions

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Starchmost common storage polysaccharide in plantscomposed of 10 30% a-amylose and 70-90% amylopectin depending on the sourcethe chains are of varying length, having molecular weights from several thousands to half a million

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Polysaccharides:Plants store glucose as amylose or amylopectin, glucose polymers collectively called starch. Glucose storage in polymeric form minimizes osmotic effects.Amylose is a glucose polymer with a(14) linkages. It adopts a helical conformation. The end of the polysaccharide with an anomeric C1 not involved in a glycosidic bond is called the reducing end.

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Amylopectin is a glucose polymer with mainly a(14) linkages, but it also has branches formed by a(16) linkages. Branches are generally longer than shown above.The branches produce a compact structure & provide multiple chain ends at which enzymatic cleavage can occur.

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Amylose and amylopectin are the 2 forms of starch. Amylopectinis a highly branched structure, with branches occurring every 12to 30 residues

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suspensions of amylosein water adopt a helical conformation

iodine (I2) can insert inthe middle of the amylosehelix to give a blue colorthat is characteristic anddiagnostic for starch

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Glycogen, the glucose storage polymer in animals, is similar in structure to amylopectin. But glycogen has more a(16) branches. The highly branched structure permits rapid glucose release from glycogen stores, e.g., in muscle during exercise. The ability to rapidly mobilize glucose is more essential to animals than to plants.

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CellulosePolymer of b-D-glucose attached by b(1,4) linkagesYields glucose upon complete hydrolysisPartial hydrolysis yields cellobioseMost abundant of all carbohydratesCotton flax: 97-99% celluloseWood: ~ 50% celluloseGives no color with iodineHeld together with lignin in woody plant tissues

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Structure of cellulose

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(in starch) (in cellulose)

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Linear structures of cellulose and chitin (2 most abundant polysaccharides)

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Products obtained from celluloseMicrocrystalline cellulose : used as binder-disintegrant in tabletsMethylcellulose: suspending agent and bulk laxativeOxidized cellulose: hemostatSodium carboxymethyl cellulose: laxativeCellulose acetate: rayon; photographic film; plasticsCellulose acetate phthalate: enteric coatingNitrocellulose: explosives; collodion (pyroxylin)

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Glycogenalso known as animal starchstored in muscle and liverpresent in cells as granules (high MW)contains both a(1,4) links and a(1,6) branches at every 8 to 12 glucose unitcomplete hydrolysis yields glucoseglycogen and iodine gives a red-violet colorhydrolyzed by both a and b-amylases and by glycogen phosphorylase

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Inulinb-(1,2) linked fructofuranoseslinear only; no branchinglower molecular weight than starchcolors yellow with iodinehydrolysis yields fructosesources include onions, garlic, dandelions and jerusalem artichokesused as diagnostic agent for the evaluation of glomerular filtration rate (renal function test)

Jerusalem artichokes

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Chitinchitin is the second most abundant carbohydrate polymerpresent in the cell wall of fungi and in the exoskeletons of crustaceans, insects and spiderschitin is used commercially in coatings (extends the shelf life of fruits and meats)

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ChitinChitin is the second most abundant carbohydrate polymerPresent in the cell wall of fungi and in the exoskeletons of crustaceans, insects and spidersChitin is used commercially in coatings (extends the shelf life of fruits and meats)

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Dextransproducts of the reaction of glucose and the enzyme transglucosidase from Leuconostoc mesenteroidescontains a (1,4), a (1,6) and a (1,3) linkagesMW: 40,000; 70,000; 75,000used as plasma extenders (treatment of shock)also used as molecular sieves to separate proteins and other large molecules (gel filtration chromatography)components of dental plaques

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Dextrinsproduced by the partial hydrolysis of starch along with maltose and glucosedextrins are often referred to as either amylodextrins, erythrodextrins or achrodextrinsused as mucilages (glues)also used in infant formulas (prevent the curdling of milk in babys stomach)

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Heteropolysaccharide: Glycosaminoglycansthey are the polysaccharide chains of proteoglycansthey are linked to the protein core via a serine or threonine (O-linked)the chains are linear (unbranched)the glycosaminoglycan chains are long (over 100 monosaccharides)they are composed of repeating disaccharides

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GlycosaminoglycansInvolved in a variety of extracellular functions; chondroitinis found in tendons, cartilage and other connective tissues

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GlycosaminoglycansA characteristic of glycosaminoglycans is the presenceof acidic functionalities (carboxylate and/or sulfates)

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Hyaluronic acid derivativesseveral products are used in the management of osteoarthritis symptomsHyalagan and Synviscothers are used as ophthalmic surgical adjuncts in cataract extractions, intraocular lens implantation, corneal transplant and retinal attachment surgery (Healon, Amvisc, AMO Vitrax)

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Glycosaminoglycans

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Pectinspectins are heteropolysaccharides found in the pulp of fruits (citrus, apples)on hydrolysis pectins yield galacturonic acid, galactose, arabinose, methanol and acetic acidpectins are composed of galactans and arabansused as gelling agents (to make jellies)

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Gumswidely used in the food and pharmaceutical industryused as: suspending agents, gelling agents, thickening agents, emulsifiers, foam stabilizers, crystallization inhibitors, adhesives, binding agentsagar, tragacanth, karaya, carrageenan, guar gum, gum arabic (acacia), furcellaran, sodium alginate, locust bean gum

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Gum tragacanth

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Bacterial cell wallprovide strength and rigidity for the organismconsists of a polypeptide-polysaccharide known as petidoglycan or mureindetermines the Gram staining characteristic of the bacteria

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Structure ofpeptidoglycan

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Cell wall of Gram-positive bacteria

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Gram-negative bacteria

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Cross-section of the cellwall of a gram-negativeorganism such as E.coli

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Lipopolysaccharide (LPS) coats theouter membrane of Gram-negativebacteria.the lipid portion of the LPS is embeddedin the outer membrane and is linked toa complex polysaccharide

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Teichoic acids are covalently linked to the peptidoglycan of gram-positivebacteria. These polymers of glycerol phosphate (a and b) or ribitol phosphate (c) are linked by phosphodiester bonds

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Mycobacterial cell wall

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Glycosylated proteinsUsually done as a post-translational processProteins can contain either O-linked oligosaccharides or N-linked oligosaccharides

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Serine or threonine O-linked saccharides

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Aspargine N-linked glycoproteins

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These glycoproteins are found inThe blood of Arctic and Antarcticfish enabling these to live at sub-zero water temperatures

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Some of the oligosaccharides found in N-linked glycoproteins

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Proteoglycans are a family of glycoproteinswhose carbohydrate moieties are predominantlyglycosaminoglycans

structures are quite diverse as are sizesexamples: versican, serglycin, decorin, syndecan

Functions: - modulate cell growth processes - provide flexibility and resiliency to cartilage

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A portion of the structure of heparinHeparin is a carbohydrate with anticoagulant properties. It is used in bloodbanks to prevent clotting and in the prevention of blood clots in patients recovering from serious injury or surgery

Numerous derivatives of heparin have been made (LMWH, Fondaparinux)

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Hyaluronate:material used tocement the cells into a tissue

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GLYCOLIPIDSCerebrosidesOne sugar moleculeGalactocerebroside in neuronal membranesGlucocerebrosides elsewhere in the bodySulfatides or sulfogalactocerebrosidesA sulfuric acid ester of galactocerebrosideGlobosides: ceramide oligosaccharidesLactosylceramide2 sugars ( eg. lactose)GangliosidesHave a more complex oligosaccharide attachedBiological functions: cell-cell recognition; receptors for hormones

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glycolipids

There are different types of glycolipids: cerebrosides, gangliosides,lactosylceramides

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GLYCOLIPIDSCerebrosidesOne sugar moleculeGalactocerebroside in neuronal membranesGlucocerebrosides elsewhere in the bodySulfatides or sulfogalactocerebrosidesA sulfuric acid ester of galactocerebrosideGlobosides: ceramide oligosaccharidesLactosylceramide2 sugars ( eg. lactose)GangliosidesHave a more complex oligosaccharide attachedBiological functions: cell-cell recognition; receptors for hormones

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Gangliosidescomplex glycosphingolipids that consist of a ceramide backbone with 3 or more sugars esterified,one of these being a sialic acid such as N-acetylneuraminic acidcommon gangliosides: GM1, GM2, GM3, GD1a, GD1b, GT1a, GT1b, Gq1b

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Ganglioside nomenclatureletter G refers to the name gangliosidethe subscripts M, D, T and Q indicate mono-, di-, tri, and quatra(tetra)-sialic-containing gangliosidesthe numerical subscripts 1, 2, and 3 designate the carbohydrate sequence attached to ceramide

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Ganglioside nomenclatureNumerical subscripts:1. Gal-GalNAc-Gal-Glc-ceramide2. GalNAc-Gal-Glc-ceramide3. Gal-Glc-ceramide

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A ganglioside (GM1)

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EMBED ChemDraw.Document.4.5

maltose

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_995895816.cdx

_995896062.cdx

_990519760.cdx

_990518035.cdx

EMBED ChemDraw.Document.4.5

cellobiose

_990519537.cdx

_990519830.cdx

_995891380.cdx

_995896183.cdx

_990519791.cdx

_990519321.cdx

EMBED ChemDraw.Document.4.5

amylose

_995894110.cdx

_1052593401.cdx

EMBED ChemDraw.Document.4.5

amylopectin

_995972862.cdx

_995973151.cdx

_995972609.cdx

EMBED ChemDraw.Document.4.5

glycogen

_995972862.cdx

_995973151.cdx

_995972609.cdx