oligosaccharides

•OLIGOSACCHARIDES POLYSACCHARIDES

CHEMISTRY OF CARBOHYDRATES- 2

DR.RITTU CHANDEL 04-09-12

CARBOHYDRATE

MONOSACCHARIDE

OLIGOSACCHARIDE

POLYSACCHARIDE

Two to ten monosaccharide units on hydrolysis

More than ten monosaccharide units on hydrolysis

HOMOPOLYSACCHARIDE

HETEROPOLYSACCHARIDE

DISACCHARIDES

• Most common among oligosaccharides• two monosaccharide units (similar or

dissimilar) held by glycosidic bonds• properties – water soluble, sweet to

taste

REDUCING

NON REDUCING

MALTOSE,LACTOSE,ISOMALTOSE,CELLOBIOSE

SUCROSE,TREHALOSE

DISACCHARIDES CONSTITUENTS

REDUCING

(+)- MALTOSE GLUCOSE+GLUCOSE(+)- LACTOSE GLUCOSE+GALACTOSE (+)-CELLOBIOSE GLUCOSE+GLUCOSE MELIBIOSE GLUCOSE+GALACTOSE

NON REDUCING(+)-SUCROSE GLUCOSE+FRUCTOSE

TREHALOSE GLUCOSE+GLUCOSE

-

MALTOSE (malt sugar)

MALTOSE

• Digestion of starch by amylase,germinating seeds, malt• Action of maltase or dilute acid on maltose gives

glucose units• Fermented by yeasts• PROPERTIES: Reducing sugar, soluble and sweet taste Sunflower shaped osazones Mutarotation Exhaustive methylation of all free –OH group,followed

by hydrolysis of glycosidic linkage gives 2,3,4,6-tetra-O-methyl-D-glucose and 2,3,6-tri-O-methyl-D-glucose

LACTOSE (MILK SUGAR)

LACTOSE

• In milk• Action of intestinal lactase on lactose gives glucose

and galactose• PROPERTIES: Reducing sugar Powder puff or hedgehog or badminton ball shaped

osazone Not very soluble and not so sweet dextrorotatory At body temperature exists as an equilibrium

mixture of α and β forms in 2:3

LACTOSE

• Fearon’s test• lactosuria

SUCROSE (TABLE SUGAR)

SUCROSE

• In sugar cane,sugar beet,pineapple,carrot roots

• Major carbohydrate in photosynthesis (in roots,tuber,seeds)

• Most abundant among naturally occuring sugars

• Distinct advantage:storage and transport forms

• Action of Intestinal sucrase on sucrose gives glucose and fructose

SUCROSE

PROPERTIES Non reducing No osazone formation Very soluble and very sweet Specific sucrose test USE Sweetening agent in food industry

INVERSION OF SUCROSE

• Dextrotatory sucrose (+66.5˚) on hydrolysis becomes levorotatory

• Equimolar mixture of glucose and fructose is invert sugar

• Honey contains invert sugar (sweeter than sucrose)

• Sucrose•

sucraseα -D-glucopyranose+112.2 ˚

β-D-glucopyranose+18.7 ˚

β -D-fructofuranose β -D-fructopyranose-133 ˚

α -D-fructopyranose-21˚

ISOMALTOSE, GENTIOBIOSE

ISOMALTOSE - Glucose + glucose α(1 → 6) partial hydrolysis of glycogen and starch gives it oligo-1,6-glucosidase in intestinal juice hydrolyses

GENTIBIOSE - β (1 → 6) glucose +glucose

TREHALOSE

Non reducing sugarDistinctive sweet tasteMajor sugar of insect endolymph

CELLOBIOSE

Virtually no tasteNot fermented by yeastObtained by hydrolysis of celluloseIndigestible by humansΒ(1→ 4) linkage is represented as zigzag but one

glucose is actually flipped over relative to other

H O

OH

H

OHH

OH

CH 2OH

H

O OH

H

H

OHH

OH

CH 2OH

H

H

H

O1

23

4

5

6

1

23

4

5

6

cellobiose

LACTULOSE

• A ketodisaccharide• Fermented by intestinal bacteria• Used in osmotic laxative, in hepatic

encephalopathyα-D-galactopyranosyl-(1 → 4)-β-D-

fructofuranose

TRISACCHARIDES

• RAFFINOSE in sugar beets• O-α-D-galactopyranosyl-(1→6)-0-α-D- glucopyranosyl -

(1→2)-β-D-fructofuranoside

• MELEZITOSEin sap of some coniferous treesO-α-D-glucopyranosyl-(1→3)-O-β-D-fructofuranosyl-(2 → 1)-α-

D-glucopyranoside

TETRASACCHARIDE

STACHYOSE Galactose+galactose+glucose+fructos

e

PENTASACCHARIDE VERBASCOSE

Galactose+Galactose+galactose+glucose+fructose

POLYSACCHARIDES(GLYCANS)

Repeat units of monosaccharides or their derivatives,held by glycosidic bonds

Relatively or totally insoluble,tasteless

LINEAR

BRANCHED

POLYSACCHARIDES

HOMOPOLYSACCHARIDE

HETEROPOLYSACCHARIDE

GLUCAN

FRUCTOSAN

MANNANS

HOMOPOLYSACCHARIDE

STORAGE POLYSACCHARIDE

STRUCTURAL POLYSACCHARIDE

STARCHGLYCOGENDEXTRANSINULIN

CHITINCELLULOSE

STARCH

STARCH

• Most important dietary source of man and animals

• Carbohydrate reserve of plants• In potato,tapioca,rice,wheat• Deposited in form of granules in

cytoplasm• STARCH GLUCOSE

Acid hydrolysis

AMYLOSE

Amyloseα(1 → 4)Not soluble in waterForms hydrated micellesGives blue colour with iodineHelical coil with 6 glucose/turn

Amylopectin α(1→4) but branching points are α(1→ 6)Most abundant in plantsGives red violet colour with iodine

AMYLASES

Two types-α and βBoth hydrolyse only α- glycosidic bondsα- amylase = α(1→4)-glucan-4-

glucanhydrolaseβ-amylase = α(1→4)-glucan-4-

maltohydrolase Debranching enzyme- α (1→6)-

glucosidase or α (1→6)- glucan-6-glucanhydrolase

BREAKDOWN PRODUCTS OF STARCH

AMYLOPECTIN VIOLET

ERYTHRODEXTRIN REDACHRODEXTRIN NO

MALTOSE NO

STARCH BLUE

GLYCOGEN

Main storage polysaccharide of animal cell

Abundant in liver and skeletal muscle

Also in plants that do not have chlorophyll

Animal starch

Immediate source of energy

Dextrorotatory

Not readily soluble in water and forms opalascent solution

Not destroyed by hot strong KOH or NaOH

With iodine gives deep red colour

GLYCOGEN

Glycogen is used as energy source,glucose units are removed one at a time from non reducing endsGlucose is not stored in monomeric formStarch and glycogen are heavily hydrated

DEXTRAN

Polymer of D-glucose Synthesized by leuconostoc mesenterides Dental plaque Synthetic dextrans Branched polysaccharide of D-glucose Branching at 1 → 2, 1 → 3, 1 → 4 or 1 → 6 Plasma volume expander

INULIN

D-fructose residues in β(2→1)In dahlia,garlic,onion,dandelionWhite, tasteless powderLevorotatoryNo dietary importance in humansUsed for estimation of body water

volume(ECF),assesing kidney functions through means of GFR

CHITIN

Second most abundant polysaccharide

CELLULOSE

Not attacked by α or β amylase

CELLULOSE

Schematic of arrangement of cellulose chains in a microfibril.

Every other glucose molecule is flipped over other due to β linkagesParallel orientation is favoured by intermolecular hydrogen bondX-ray diffraction of cellulose shows bundles of parallel chains to form fibrils

Not digested by mammals

CELLULOSE

Most abundant structural polysaccharide in plants

Cotton fibers are pure celluloseInsoluble in water D-glucose CELLULOSE partial hydrolysis Cellobiose

2,3,6-tri-O-methyl glucose

Complete hydrolysis

Exhaustive methylation

Strong acids

BIBLOGRAPHY

LEHNINGERHARPERTALWARBHAGVANDEBJYOTI DAS

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