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Abdullah zreqat

Bahaa Najjar

Mamoon Ahram

Polysaccharides Definition and Structure

Polysaccharides [Greek poly = many; sacchar = sugar] are complex carbohydrates, composed of 10 to

up to several thousand monosaccharides arranged in chains. The most common monosaccharides that

appear as parts of polysaccharides are glucose, fructose, galactose and mannose.

When all the monosaccharides in a polysaccharide are the same type, the polysaccharide is called a h

omopolysaccharide or homoglycan, but when more than one type of monosaccharide is present they ar

e called heteropolysaccharides or heteroglycans

*let us continue with another sugar :

dextran

* A storage polysaccharide

-(1-6)-D-glucose with branched chains

*Branches: 1-2, 1-3, or 1-4

*dextran work as mashwork ,because it's monomers are large with branches

* bectiria Use dextran for nutrition and cause Dental caries Because it isolates teeth

From washing

£*Cellulose(Fibers) "homopolemer"

Cellulose is an organic compound .Apolysaccharide consisting of a linear chain of several

hundred to many thousands of β(1→4) linked D-glucose units only.

*Some animals, particularly ruminants and termites, can digest cellulose with the help of symbiotic

micro-organisms that live in their guts. In human nutrition, cellulose acts as a hydrophilic bulking ag

ent for feces and is often referred to as dietary fiber.

*note : Humans can not digst this sugar Because they don't have cellulose enzyme.

Important note : when huma eat cellulose bind to toxic substance in foods , they get exported from the

body , thus preventing them damaging the lower intestine or being reabsorbed there .

example : 1- when bind to carcinogens , thus prevent cance .

2- when bind to cholesterol resulting in less amount in the blood .

Note: cellulose is rigid and straight .

*pectin (from plants cell wall):**

_Forms by D-galacturinic aCids " galactrunic acid is a galactose derivative "

Alpha

*chitin ( Finds in Exoskeleton in insects ):

*Structure of the chitin molecule, showing two of the N-acetylglucosamine units that repeat to form long

chains in β-(1→4)-linkage

Note : repeating in disaccharide in chain

Note :chitin is strength because of hydrogen bonds between strands .

Note : glycogen , cellulose , pectin and chitin are not reducing molecule .

Another point about glycosides is worth mentioning. We have already seen that the anomeric carbon is

frequently involved in the glycosidic linkage, and also that the test for the presence of sugars—specific

ally for reducing sugars—requires a reaction of the group at the anomeric carbon. The internal anomeri

c carbons in oligosaccharides are not free to give the test for reducing sugars. Only if the end residue is

a free hemiacetal rather than a glycoside will there be a positive test for a reducing . The level of detec

tion can be important for such a test. A sample that contains only a few molecules of a large polysacch

aride, each molecule with a single reducing end, might well produce a negative test because there are

not enough reducing ends to detect. Only 1 carbon can Play as reducing sugar But this carbon makes

branche, not 4carbon

Glycosaminoglycans

Feature :

They contain amino group " amino sugers"

Made of repeated of disaccharide

These are negatively charged molecule

Some of these have sulfate group or carboxylic group

Found in outside of the cells

*GlYcosaminoglycan(GAG'S):

*Glycosaminoglycans (GAGs) or mucopolysaccharides.are long unbranched polysaccharides consistin

g of a repeating disaccharide unit

*. The repeating unit (except for keratan) consists of an amino sugar (N-acetylglucosamine or N-acetylg

alactosamine) along with a uronic sugar (glucuronic acid or iduronic acid) or galactose

.*Glycosaminoglycans are highly polar and attract water

*. They are therefore useful to the body as a lubricant or as a shock absorber.

*proteoGlycans:

*Glycoproteins contain carbohydrate residues in addition to the polypeptide chain .Some of the most im

portant examples of glycoproteins are involved in the immune response; for example, antibodies, bact

erial cell wall, which bind to and immobilize antigens (the substances attacking the organism), are glyc

oproteins. Carbohydrates also play an important role as antigenic determinants, the portions of an antig

enic molecule that antibodies recognize and to which they bind.

O_glycosidic or N_glycoside depend on nature of amino acid (where proteins attach with some of

sugers)

*Peptideoglycan:

**Sialic acid is a generic term for the N- or O-substituted derivatives of neuraminic acid, a monosacchar

ide with a nine-carbon backbone.

*Sialic acids are found widely distributed in animal tissues and to a lesser extent in other organisms, ra

nging from plants and fungi to yeasts and bacteria, mostly in glycoproteins and gangliosides (they occu

r at the end of sugar chains connected to the surfaces of cells and soluble proteins).

*Importancs Of cellelose:

1)helps move the digested food through the intestines, decreasing the transit time through the gut.

2)Potentially toxic substances in food and in bile fluid bind to fiber and are exported from the body, thus

preventing them from damaging the lower intestine or being reabsorbed there.

3)People on high-fiber diets also tend to take in less fat and fewer calories.

4)There has been much publicity about fiber in the diet reducing cholesterol.

Fiber does bind cholesterol, and it certainly causes some decrease in the amount in the blood. The red

uction, expressed as a percentage, is higher in cases in which the original level of cholesterol is higher.

There is, however, no definitive evidence that lowering cholesterol via the ingestion of fiber results in le

ss heart disease

Sorry for any mistakes