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Chemistry of
Polysaccharides
1
Carbohydrates 5
General Program
Prof. Dr. Abeer Gaffer Ali Hassan
Biochemistry Department
Veterinary Medicine, Suez Canal University

 Characteristics:
 Polymers (MW from 200,000) of monosaccharides or/and
their derivatives with high molecular weight.
 White and amorphous products (glassy)
 not sweet
 not reducing; do not give the typical aldose or ketose reactions.
 form colloidal solutions or suspensions
 They classified into
 Homopolysaccharides (Homoglycans): polymers of a
single type of sugar or derived monomers e.g. Starch,
Cellulose, Glycogen, Dextrins, Chitin or Inulin)
 Heteropolysaccharides (Heteroglycans): polymers of more
than one type of sugar or derived sugar monomers
(Mucopolysaccharides)
2
Polysaccharides or glycans

 Homopolysaccharides are polymers composed of a single type of sugar
monomers. It may be classified according to type of sugar or according to
its significance inside the body into
Homopolysaccharides
classified according
to type of sugar
into:
Glucosans
e.g. Starch, Cellulose
Fructosan
e.g. Inulin
Galactosan
e.g. Agar
classified according
to its significance
inside the body into
Structural
e.g. Cellulose, Chitin
Storage
e.g. Starch, Glycogen, Inulin , Dextrin,
Dextran
Homopolysaccharides

 Storage polysaccharides are important carbohydrate
forms in plants and animals.
 It seems likely that organisms store carbohydrates in the
form of polysaccharides rather than as monosaccharaides to
lower the osmotic pressure of the sugar reserves
 Because, osmotic pressure depends only on numbers of
molecules
– Hence, the osmotic pressure is greatly reduced by formation of
a few polysaccharide molecules out of thousands (or even
millions) of monosaccharide units
 E.g. Starch , Glycogen, Dextrin, Dextran, Inulin
4
Storage Polysaccharides

 Starch is the most common storage polysaccharide in Plants
which has two components:
 α-amylose
 amylopectin
 Most forms of the starch in nature contain 10-30% α-amylose
and 70-90% amylopectin
 α -Amylose is composed of linear chains of D-glucose in α(1-4)
linkages. The chains are of varying lengths, having molecular
weights from several thousand to half a million
 The chain has a reducing end and a non-reducing end
5
H O
OH
H
OH
H
OH
CH2OH
H
O H
H
OH
H
OH
CH2OH
H
O
H
H H O
O
H
OH
H
OH
CH2OH
H
H H O
H
OH
H
OH
CH2OH
H
OH
H
H O
O
H
OH
H
OH
CH2OH
H
O
H
1
6
5
4
3
1
2
amylose
Reducing end
α 1,4 glycosidic link
Non-Reducing end
1 Starch

6
α -Amylose :
o It is easily digested by α- amylase
(salivary or pancreatic)
o Although it is poorly soluble in
water, soluble in hot water α -
amylose forms micelles in which
the polysaccharide chain has a
helical conformation.
o Iodine reacts with α-amylose to
give a characteristic blue colour,
due to insertion of iodine into the
middle of the hydrophobic amylose
helix

Amylopectin:
➢ The other component of typical starches, is a highly branched chain
of glucose units
➢ The linear linkages in amylopectin are α(1-4), whereas the branch
linkages are α(1-6)
➢ The average branch length is between 24 and 30 residues, and
molecular weights of amylopectin molecules can reach up to millions.
➢ It is only digested by pancreatic α- amylase.
➢ As is the case for α-amylose , amylopectin forms micellar suspensions
in water. It produce a red-violet colour with Iodine.
7
H O
OH
H
OH
H
OH
CH2OH
H
O H
H
OH
H
OH
CH2OH
H
O
H
H H O
O
H
OH
H
OH
CH2
H
H H O
H
OH
H
OH
CH2OH
H
OH
H
H O
O
H
OH
H
OH
CH2OH
H
O
H
O
1 4
6
H O
H
OH
H
OH
CH2OH
H
H H O
H
OH
H
OH
CH2OH
H
H
O
1
OH
3
4
5
2
amylopectin
α 1,6 glycosidic link

 Also known as animal starch
-Stored in muscle and liver
-Present in cells as granules (high MW)
-Contains both α(1,4) links and α (1,6) branches at every 8
to 12 glucose unit
-Complete hydrolysis yields glucose
- With iodine gives a red-violet color
-Hydrolyzed by both α and β-amylases and by glycogen
phosphorylase

8
2 Glycogen

 In the liver, glycogen synthesis and degradation are
regulated to maintain blood-glucose levels as required
to meet the needs of the organism as a whole.
Glycogen serves as a buffer to maintain blood glucose
level.
 In contrast, in muscle, these processes are regulated
to meet the energy needs of the muscle itself.
 The concentration of glycogen is higher in the liver
than in muscle (6-8 % versus 2% by weight), but more
glycogen is stored in skeletal muscle overall because
of its much greater mass.
9
Structure of Glycogen
2 Glycogen

 Produced by the partial hydrolysis of starch along with
maltose and glucose
-Dextrins are often referred to as either amylodextrins,
erythrodextrins or achrodextrins
-Used as mucilages (glues)
-Used in infant formulas
- Also Used as thickening agents in food processing
10
3 Dextrins

11
• is a polysaccharide similar to
amylopectin, but the main
chains are formed by 1α→6
glycosidic linkages and the side
branches are attached by 1α→3
or 1α→4 linkages.
• it is glucose units Contains α
(1,4), α(1,6) and α (1,3) linkages
• MW: 40,000; 70,000; 75,000
• Dextran is synthesized from
sucrose by certain lactic acid
bacteria, the best-known
being Leuconostoc mesenteroides.
4 Dextran

 Dextran is an oral bacterial
product that adheres to the
teeth, creating a coating film
called plaque.
 It is also used commercially in
confections, in lacquers, as food
additives.
 It has antithrombotic effect.
 Used as plasma expanders
(treatment of shock)
12
o also used as molecular sieves to separate proteins and other
large molecules (gel filtration chromatography)
4 Dextran

❖ β-(1,2) linked fructofuranoses, have a
terminal glucose.
-Linear ,no branching
-Lower molecular weight than starch
-Colors yellow with iodine
❖ Sources include onions, garlic, dandelions
and Jerusalem artichokes
❖ Inulin is soluble in warm water and has a
smooth creamy texture that provides a
fat-like mouth feel.
❖ Inulin is non digestible by human
intestinal enzymes, but they are totally
fermented by colonic microflora.
13
5 Inulin (Fructosan)
β-(1,2)

USES OF INULIN
 used clinically as a highly accurate
measure for the evaluation of glomerular
filtration rate (GFR) (renal function test).
Using inulin to measure renal function is
the "gold standard" for comparison with
other means of estimating creatinine
clearance.
 - Used as a soluble dietary fiber
- Used as appetite suppressant
- Used as a low glycemic index sweetener
-Also used as a fat/cream substitute
14

Structural
HomoPolysaccharides
17

18
a major constituent of plant cell walls, consists of long linear chains
of glucose with b(1→4) linkages.
Every other glucose is flipped over, due to b linkages.
cellulose
H O
OH
H
OH
H
OH
CH2OH
H
O
H
OH
H
OH
CH2OH
H
O
H H O
O H
OH
H
OH
CH2OH
H
H O
H
OH
H
OH
CH2OH
H
H
OH
H O
O H
OH
H
OH
CH2OH
H
O
H H H H
1
6
5
4
3
1
2
This promotes intra-chain and
inter-chain H-bonds and
van der Waals interactions, that
cause cellulose chains to be
straight & rigid, and pack with a
crystalline arrangement in thick
bundles - microfibrils. Schematic of arrangement of
cellulose chains in a microfibril.
1 Cellulose
b(1→4)

These microfibrils are very strong.
The role of cellulose is to impart strength and rigidity to
plant cell walls, which can withstand high hydrostatic
pressure gradients. Osmotic swelling is prevented.
17
1 Cellulose

 Yields glucose upon complete hydrolysis -Partial hydrolysis yields
cellobiose
 Most abundant of all carbohydrates
Gives no color with iodine. Cellulose is tasteless, odorless and
insoluble in water and most organic solvents.
 Mammals lack any enzyme (cellulase) that hydrolyzes the β 1→ 4
bonds, and so cannot digest cellulose. It is an important source of
"bulk" in the diet, and the major component of dietary fiber.
 Microorganisms in the gut of ruminants and other herbivores can
hydrolyze the linkage and ferment the products to short-chain fatty
acids as a major energy source.
 Even wood termites depend on certain protozoa in its gut to digest
cellulose 18
1 Cellulose

SIGNIFICANCE OF CELLULOSE
 Microcrystalline cellulose : used as binder in tablets
 Methylcellulose: suspending agent and bulk laxative
Oxidized cellulose: hemostat
Sodium carboxy-methyl cellulose: laxative
Cellulose acetate phthalate: enteric coating
 Cellulose acetate: rayon; photographic film; plastics
Nitrocellulose: explosives; collodion (pyroxylin)
19

➢ polymer of N- Acetyl Glucosamine (b(1→4) glycosidic
bonds)
➢ Chitin is the second most abundant carbohydrate,
Present in the cell wall of fungi and in the exoskeletons of
crustaceans, insects and spiders, serves as a protection
from water in insects.
➢ Chitin is used commercially in coatings (extends the shelf
life of fruits and meats
➢ Chitin is also used to waterproof paper, and in cosmetics
and lotions to retain moisture.
➢ Chitin is used as surgical thread that biodegrades as a
wound heals.
20
2 Chitin

Heteropolysaccharides
21
Heteropolysaccharides are polymers
composed of more than one type of
sugar or derived sugar monomers. It
may be classified into:

Heteropolysaccharides
Others in Plants &
M.O.
*Mucilages
*Agar
*Vegetable
gums
*Pectins
*Hemicellulose
Glycosaminoglycans (GAGs)
(Mucopolysaccharides)
Glycoproteins
(mucoproteins)
neutral
Blood groups
Proteoglycans
Fairly acidic
*Hyaluronic acid
*Chondroitin Sulfate
*Dermatan sulfate
*Keratan sulfate
*Heparin
22

❖ Mucilage:
is a thick, gluey substance produced by nearly all plants and some M.Os.
(microorganisms). It is a polar glycoprotein and an exopolysaccharide.
Mucilage in plants plays a role in the storage of water and food, seed
germination, and thickening membranes
❖ Gum arabic: also known as acacia gum,
1. is a natural gum made of the hardened sap ‫العصارة‬ of various species of
the acacia tree.
2. gum arabic is complex mixture of glycoprotein and polysaccharide. It is the
original source of the sugars arabinose and ribose but contain also
galactose and glucuronic acid.
❖ Pectins:
1. are structural Heteropolysaccharides contained in cell wall of plants.
they are rich in galacturonic acid with D-galactose, L-arabinose and D-
xylose.
2. mainly extracted from citrus fruits, and is used in food as a gelling agent,
particularly in jams and jellies. It is also used in fillings, sweets, as a
stabilizer in fruit juices and milk drinks, and as a source of dietary fiber.
3. In medicines, used to treat noninfectious diarrhea in infants.
23

❖ hemicellulose (known as polyose)
1. is any of several heteropolymers (matrix polysaccharides),
such as arabinoxylans.
2. besides glucose, sugar monomers in hemicellulose can
include xylose, mannose, galactose , rhamnose and
arabinose .
3. Hemicelluloses contain most of the D-pentose sugars, and
small amounts of L-sugars as well as sugar acid glucuronic
and galacturonic.
4. It present along with cellulose almost all plant cell wall.
hemicellulose has a random, amorphous structure with little
strength. It is easily hydrolyzed by dilute acid or base and
hemicellulase enzymes.
5. It has shorter chains – 500–3,000 sugar units as opposed to
7,000–15,000 glucose molecules per polymer seen in cellulose
24

❖ AGAR (GALACTOSAN)
 Agar is a galactose polymer
-Obtained from the cell walls of some species of red
algae or seaweeds (Sphaerococcus Euchema ) and
species of Gelidium
 Agar is actually the resulting mixture of two
components: the linear polysaccharide agarose, and a
heterogeneous mixture of smaller molecules
called agaropectin
 Dissolved in hot water and cooled, agar becomes
gelatinous;
-Its chief use is as a culture medium for
microbiological work.
-Other uses are as a laxative,
-A vegetarian gelatin substitute,
-A thickener for soups, in jellies, ice cream and
Japanese desserts,
-As a clarifying agent in brewing, and for sizing fabrics.
26

GLYCOSAMINOGLYCANS (GAGS)
(MUCOPOLYSACCHARIDES)
❖ Proteoglycans (Fairly acidic)
❖ Glycosaminoglycans of physiological Significance
 *Hyaluronic acid *Chondroitin Sulfate
 *Dermatan sulfate *Keratan sulfate *Heparin
 They are carbohydrate polymers containing a repeating disaccharide.
 The disaccharide usually contains an acid sugar and an amino
sugar.
 Acid sugar is generally D- Glucuronic acid or its C-5 epimer
Iduronic acid except Keratan sulfate.
 While amino sugar is either D- Glucosamine or D-Galactosamine,
amino group is generally acetylated eliminating its positive charge.
 The amino sugar may be sulfated on non acetylated nitrogen except
Hyaluronic acid.
 Carboxyl groups of acid sugars together with sulfate groups give
Glycosaminoglycans the negative nature.
27

HYALURONIC ACID (D-GLUCURONATE + GLCNAC)N

β-D glucuronic acid + N- Acetyl Glucosamine (b(1→3) glycosidic
bonds)
 Occurrence: Umbalical cord, vitreous humer (fluid of eye),
synovial fluid, ECM of loose connective tissue as cement
substance of tissue.
 Hyaluronic acid polymers are very large (100 - 10,000 kDa) and
can displace a large volume of water. It coiled and entwined
making very firm gel, hinder spread of bacterial infection.
 Serves as a lubricant and shock absorber.
Hyaluronic acid is unique
because it does not contain
any sulfate and is not found
covalently attached to
proteins.
It forms non-covalently linked
complexes with Proteoglycans
in ECM.
β-1,3
glycosidic
link

HYALURONIC ACID
 hyaluronidase enzyme which hydrolysis the hyaluronic
acid produced by bacteria and snake venom.
 It is also important in process of fertilization where
sperm is rich in the enzyme for penetration of ovum.
 The hyaluronic acid that is used as medicine is extracted
from rooster combs or made by bacteria in the laboratory.
 The FDA has also approved the use of hyaluronic acid for
injection into the knee for patients with knee
osteoarthritis and used also for other eye injuries, etc.
29

 Dermatan sulfate
(L-Iduronate + GalNAc sulfate) n
Occurrence: skin, blood vessels, heart valves, tendons, and lungs.
 Chondroitin sulfate
(D-glucuronate + GalNAc sulfate)n
Occurrence: cartilage, tendons, ligaments, heart valves and aorta.
It is the most abundant GAGs.
30
β-L iduronic acid + N- Acetyl β-D,
Glactosamine, 4- sulfate (b(1→3) glycosidic
bonds)
Type A : β-D glucuronic acid + N-
Acetyl β-D, Galactosamine, 4- sulfate
(b(1→3) glycosidic bonds)
Type C: N- Acetyl β-D, Glactosamine,
6-sulfate is the only difference
β-1,3
glycosidic
link
β-1,3
glycosidic
link

 Keratan sulfate
(Gal + GlcNAc sulfate) n
 Occurrence: cornea, bone, cartilage; muscle
Keratan sulfates are often aggregated with Chondroitin
sulfates.
 It is of 2 types: I & II
 I: present in cornea attach to aspargine of the polypeptide
chain
 II: present in muscles attach to serine and threonine of
the polypeptide chain
31
β-D galactose + N- Acetyl β-D
Glucosamine, 6 sufate (b(1→4)
glycosidic bonds)
β-1,4
glycosidic
link

❖ Heparin
(D-glucuronate sulfate + N-sulfo-D-glucosamine) n
 α-D glucuronic acid, 2 sulfate + N- sulfated Glucosamine, 6 sulfate
((1→4) glycosidic bonds)
 it contain L-iduronic sulfate 90% or glucuronic 10%
 Occurrence: it is component of intracellular granules of mast cells
lining the arteries of the lungs, liver and skin (Contrary to other
GAGs that are extra cellular compounds, it is intracellular). Acts as
an anticoagulant.
 Heparin is a medically important polysaccharide because it prevents
blood coagulation in the bloodstream.
32
o Heparan sulfate :
Heparans have less sulfate
groups than heparins. It
present in basement
membranes, component of cell
surfaces
α-1,4
glycosid
ic link

PROTEOGLYCANS
 are formed of glycosaminoglycans (GAGs) covalently attached to the
core proteins.
 are found in all connective tissues, extracellular matrix (ECM) and on
the surfaces of many cell types.
 As example: A Proteoglycan monomer found in cartilage consists of a
core protein to which the linear GAG chains are covalently linked. -
These chains which each may be composed of more than 100
monosaccharides, extend out from the core protein and remain
separated from each other because of charge repulsion. The resulting
structure resembles a ‘Bottle brush.
33
In cartilage, the
species of GAGs
include
Chondroitin sulfate
and Keratan
sulfate.

 The proteoglycan monomers associate with a molecule of
Hyaluronic acid to form Proteoglycan aggregates.
-The association is not covalent, but occurs primarily
through ionic interactions between the core protein and
Hyaluronic acid. -The association is stabilized by
additional small proteins called Link proteins.
34

FUNCTIONS OF PROTEOGLYCANS
 Act as constituent of extracellular matrix or ground substance - Interact
with collagen and Elastin
- in ECM act to attract water.
-Act as barrier in the tissues
-Act as lubricant in the joints
- Help in the release of hormones
 Help in cell migration in embryonic tissues
 Present in the basement membrane of glomerulus of kidney, play
important role in the Glomerular filtration
 Heparin acts as an anticoagulant .
-Heparin helps in the release of lipoprotein lipase, also called ‘Clearing
factor’.
 Components of cell membrane, act as receptors.
 Chondroitin sulfates and hyaluronic present in cartilages have a great role
in compressibility of cartilage in weight bearing
 In eye:
- Maintain shape of sclera
- Help in maintaining the transparency of cornea
35

NEUTRAL MUCOPOLYSACCHARIDES
GLYCOPROTEINS (MUCOPROTEIN)
 Constituent:
 Mannose (Man), Galactose (Gal), N-acetyl glucosamine (GLCNAC) -
N-acetyl galactosamine (GalNAC), arabinose (Ara), Xylose (Xyl), L-
fucose (Fu), N-acyl derivatives of neuraminic acid (NeuAC), the
predominant sialic acid.
 In contrast to the proteoglycans, uronic acid is absent
 The carboportion of glycoproteins differ from that of proteoglycans
in that it is shorter and branched
 The carbohydrate may be attached to protein via the hydroxyl
groups of serine and threonine residues or the amide N of
asparagine.
36

Physiological function of glycoproteins:-
1. Structural molecules (e.g. components of cell wall and
membrane).
2. Cell attachment and recognition sites - They are involved in
cell-cell interaction.
3. Lubricants (e.g. components of mucus).
4. Certain hormones (e.g. gonadotropin, thyrotropin, human
chorionic gonadotropin (hcG)
5. They serve as enzymes (blood clotting enzymes and lysosomal
enzymes)
6. Immunologic components (immunoglobulins, complement,
interferon).
7. As blood group substances.
8. Also found in egg protein- ovalbumin
9. Found in Pneumococci capsule
37

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