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POLYSACCHARIDES
By
SANGH PARTAP
Department of Pharmacy
Teerthanker Mahaveer University, Moradabad,
U.P., INDIA
Definition
 Polysaccharides are high molecular weight polymers
build up by repeated condensation of polyhydroxy
aldehydes/ polyhydroxy ketones which are joined
together by glycosidic linkages, and can be hydrolysed
to a large no. of monosaccharides.
EXAMPLES ARE
 CELLULOSE
 INULIN
 STARCH
 CHITIN
 HEPARIN
 HYALURONIC ACID
Types of Polysaccharides
 Homopolysaccharides :-also called as homoglycans.
On hydrolysis yield only one type of monosaccharide unit.
Example- cellulose, inulin, starch etc.
 Heteropolysaccharides :- also called as heteroglycans.
On hydrolysis yield more than one type of monosaccharide
unit.
Example- α- heparin, hyaluronic acid etc.
Cellulose
 Cellulose is the chief constituent of the cell wall
Of plant and most widely distributed carbohydrate.
 Cellulose is an organic compound with the formula
(C6H10O5)n, a polysaccharide consisting of a linear chain
of several hundred to over ten thousand β(1→4) linked Dglucose units.
Types of cellulose
 α- Cellulose :- is very much less degraded and does not
dissolve in aqueous NaOH.
 β- Cellulose:- is soluble in aqueous NaOH but insoluble in
dill. Acid.
 γ- Cellulose:- is insoluble in both.
Cellulose
Structure and properties
 Cellulose has no taste, is odorless, is hydrophilic, is
insoluble in water and most organic solvents.
1. Mol.formula of Cellulose has been found to be
(C6H10O5)n from analytical data.
2. When Cellulose is hydrolysed with fuming HCL
it give D- glucose in 95-96% yield.This reaction
reveal that Cellulose is made up of glucose unit.It
means that the structure of Cellulose is based on
the D- glucose unit.
Methylation,acetylation and nitration of Cellulose
produce trisubstitution product as a max. substituted
product, it means that each glucose unit present possesses
3 OH group in an uncombined state.
 Fully methylated cellulose, when subjected to hydrolysis yield 2,3,6 tri-
O-methyl D- glucose (90%) as main product and also 2,3,4,6 tetra-Omethyl D- glucose 0.6% as minor product.
Chemical method
 Determination of the proportion of end group and
comparing with the total no. of unit in molecule.
Haworth methylation method:Cellulose is completely methylated in inert atmosphere
then methylated cellulose is hydrolysed by dill. Acid to
cleave the glycosidic linkage.the nonreducing end will yield
2,3,4,6 tetra-O-methyl D- glucose whereas all other will
undergo hydrolysis to yield 2,3, tri-O-methyl D- glucose.
The two hydrolytic product are seprated by
chromatographic tech.
Hence by knowing the % of tetra methyl derivative or ratio
of tetra methyl- tri methyl derivative.
This method is known as the end-group assay.
Periodic oxidation method
 When cellulose is treated with sodium periodate or
periodic acid,two mole of formic acids are obtained
from reducing end whereas one mole of formic acid
from the non-reducing end.
the amount of formic acid is estimated by the titration
method. This estimation gives the value of chain
length.
Starch
 Starch is a carbohydrate consisting of a large number
of glucose units joined together by glycosidic bonds.
This polysaccharide is produced by all green plants as
an energy store.
 It is the most important carbohydrate in the human
diet and is contained in such staple foods as potatoes,
wheat, maize (corn), rice, and cassava.
 Pure starch is a white, tasteless and odorless powder that
is insoluble in cold water or alcohol.
 It is produced in the green plant by the reaction b/w water
and oxygen under catalytic effect of chlorophyll and
sunlight.
 It consists of two types of molecules:
 the linear and helical amylose:-Amylose is a linear
polymer made up of D-glucose units.
 the branched amylopectin: Branching takes place with
α(1→6) bonds occurring every 24 to 30 glucose units.
 Depending on the plant, starch generally contains 20 to
25% amylose and 75 to 80% amylopectin.
Constitutions of amylose
 It is empirical formula is C6H10O5 .
 On complete hydrolysis amylose give D-glucose units
.this indicate that amylose is composed of only D-glucose
units.
 Enzymatic hydrolysis amylose give maltose. Maltose is 4-o-
(α-glucopyranosyl) –D-glucopyranose, all the glucose unit in
starch are linked through C1α and C4. hence amylose
posesses the foolowing str. Which explain the hydrolysis
product.
 The amylose is confirmed by hydrolysis of its fully
methylated derivative to 2,3,6 tri-o-methyl-D-glucopyranose
and 0.32% of 2,3,4,6 tetra-o-methyl-D-glucopyranose
Constitution of amylopectin
 Its empirical formula is C6H10O5
 On complete hydrolysis amylopectin give D-glucose
units .this indicate that amylose is composed of only Dglucose units.
 Fully methylated amylopectin on hydrolysis gives 2,3,6
tri-o-methyl-d-glucose and 0.32% of 2,3,4,6 tetra-omethyl-d-glucose.
Differences between starch & cellulose
STARCH
It is reserve food material
of plant and is found
mainly in seeds, roots and
tubers of the plant. Wheat
, maize, patatoes and rice
are its main commercial
source.
2. It can be separated in two
components, amylose and
amylopectin.
1.
CELLULOSE
1. It
is
very
widely
distribution in nature as the
chief component of wood
and plant fibres. Cotton,
wood and juite are its main
source.
2. It
is single compound
which can not be separated
into or more components.
STARCH
CELLULOSE
3. Both
amylose
and
amylopectin consists of D-(+)
glucose unit linked through αglucoside linkage.
3. It is also made up of D-(+)
4. It gives blue colour with
4. It does not give blue colour
iodine.
glucose unbrached chain but
they are interlinked by βglucoside linkage.
with iodine.
CHITIN
Linear homopolysaccharide composed of N-acetyl
glucosamine residues in linkage
The only chemical difference from cellulose is the
replacement of the hydroxyl group at C-2 with an acetylated
amino group.
Chitin forms extended fibers similar to those of cellulose,
and like cellulose cannot be digested by vertebrates.
Chitin is the principal component of the hard exoskeletons
of nearly a million species of arthropods—insects, lobsters,
and crabs, for example— and is probably the second most
abundant polysaccharide, next to cellulose, in nature.
Chitin
Hetropolysaccharides
 Hyaluronic acid
 Heparin
 Agarose
Hyaluronic acid
Hyaluronic acid is an important GAG
(Glycosamonoglycan) found in the ground substance of
synovial fluid of joints and vitreous humor eye.
serves as a lubricant and shock absorbant in joints.
composed of alternate unit of D-gluconic acidN-acetyl Dglucosamine.
Heparin
 Heparin is an anticoagulant( prevant blood clothing)
produced by basophils and mast cells that occur in
blood, lung, liver, kidney, spleen etc.
 Heparin is composed of alternate unit of N-sulfo Dglucosamine 6-sulfate and glu 2-sulfate.
Agarose
The repeating unit consists of D-galactose (β 1 4)-linked to
3,6-anhydro-L-galactose (in which an ether ring connects C-3
and C-6). These units are joined by ((α1 3)-) glycosidic links
to form a polymer 600 to 700 residues long. A small fraction
of the 3,6-anhydrogalactose residues have a sulfate ester at
C-2.
Uses
Agarose gels are used as inert supports for the electro phoretic separation of nucleic acids, an essential part of the
DNA sequencing process .
Agar is also used to form a surface for the growth of
bacterial colonies.
Another commercial use of agar is for the capsules in which
some vitamins and drugs are packaged; the dried agar
material dissolves readily in the stomach and is metaboli- cally inert.
SUMMARY
Polysaccharides (glycans) serve as stored fuel and as
structural components of cell walls and extracellular matrix.
The homopolysaccharides starch and glycogen are stored
fuels in plant, animal, and bacterial cells. They consist of Dglucose with linkages, and all three contain some branches.
■
The homopolysaccharides cellulose, chitin, and dextran
serve structural roles. Cellulose, composed of (1n4)-linked Dglucose residues, lends strength and rigidity to plant cell
walls. Chitin, a polymer of (1n4)-linked N-acetylglucosamine,
strengthens the exoskeletons of arthropods. Dextran forms an
adhesive coat around certain bacteria.
■
Homopolysaccharides fold in three dimensions. The chair
form of the pyranose ring is essentially rigid, so the
conformation of the polymers is determined by rotation
about the bonds to the oxygen on the anomeric carbon.
Starch and glycogen form helical structures with intrachain
hydrogen bonding; cellulose and chitin form long, straight
strands that interact with neighboring strands.
■ Bacterial and algal cell walls are strengthened by heteropolysaccharides—peptidoglycan in bacteria, agar in red
algae. The repeating disaccharide in peptidoglycan is
GlcNAc(1n4)Mur2Ac; in agarose, it is D-Gal(1n4)3,6anhydro-L-Gal.
 Glycosaminoglycans
are extracellular heteropolysacch-
arides in which one of the two monosaccharide units is a
uronic acid and the other an N-acetylated amino sugar.
Sulfate esterson some of the hydroxyl groups give these
polymers a high density of negative charge, forcing them to
assume
extended
conformations.
These
polymers
(hyaluronate, chondroitin sulfate, dermatan sulfate, keratan
sulfate, and heparin) provide viscosity, adhesiveness, and
tensile strength to the extracellular matrix.