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Notes prepared by
Keven Liam William
1st Msc Zoology
St. Albert’s College(Autonomous), Ernakulam1
• They are repeating units of monosaccharides or their
derivatives held together by glycosidic bonds.
• They are simply known as glycans.
• They can be straight chain of monosaccharides known as
linear polysaccharides or it can be branched known as
• They are not sweet in taste
• They do not form crystals.
• They are carbohydrates with high molecular weight.
Classification of polysaccharides
• Polysaccharides that contains the same type of monosaccharide units
are known as homopolysaccharides.
• Glucans are polymers of glucose and fructosans are polymers of
• Examples :
– Glucosan – Starch, Glycogen, cellulose
– Fructosan – Insulin
– Galactosan - Agar
• It is a storage polysaccharide and the most common
polysaccharide seen in plants
• It is a homopolymer composed of D – glucose units held
by alpha – glycosidic linkage.
• Composed of 10 – 30% Amylose and 70 – 90%
Amylopectin depending on the source.
• They can be hydrolysed into simpler carbohydrates by
acids, various enzymes or a combination of the two. The
resulting fragments are known as dextrin.
• It is a straight long unbranched chain polymer composed of 250 –
300 D – glucose units held by α (1-4) glycosidic linkage.
• It is less soluble in water
• Gives a dark blue/black colour when iodine solution is added
• Amylopectin is a branched chain polymer of D – glucose
• It is more soluble in water
• Gives a reddish brown colour when iodine solution is
• Branched chain with α (1-6) glycosidic bonds at the
branching points and α (1-4) glycosidic bonds in the
• It contains few thousand glucose units looks like a
branched tree (20-30) glucose units per branch.
• It is also known as animal starch.
• It is stored in the muscles and liver.
• It is present in plants with no chlorophyll (eg: yeast, fungi)
• Structure of glycogen is similar to that of amylopectin with more
number of branches.
• Glucose is the repeating unit in glycogen joined together with by
α (1-4) glycosidic bonds and α (1-6) glycosidic bonds at
• Present in cells as granules with high molecular weight.
• Complete hydrolysis yields glucose
• Glycogen serves as a buffer to maintain the blood glucose level.
• The concentration of glycogen is higher in the liver than in
muscle, but more glycogen is stored in the skeletal muscle
overall because of its much greater mass.
• Polymer of β – D – Glucose linked by β (1-4) linkages.
• Complete hydrolysis yields glucose and partial hydrolysis yields
• Cellobiose is made up of two molecules of D – glucose linked by
β – glucosidic linkages between C1 and C4 of adjacent glucose
• It is the most abundant of all carbohydrates.
• Gives no colour with iodine.
• It is tasteless, odourless and insoluble in water and most organic
• Herbivorous animals utilise cellulose with the help of bacteria.
• Human beings lack any enzyme 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 stimulating
peristalsis and elimination of indigestible food residues.
• It is a linear homopolysaccharide composed of N –
acetyl glucosamine in β – linkage.
• Only difference from cellulose is the replacement of the
hydroxyl group at C – 2 with an acetylated amino group.
• It is the principal component of hard exoskeleton of
arthopods and present in the cell wall of fungi.
• Second most abundant in nature
• It is produced by the partial hydrolysis of starch
along with maltose and glucose.
• They are often referred to as either amylodextrins,
erythrodextrins or achrodextrins.
• They are used as mucilages (glues)
• They are used in infant formulas.
• Indigestible dextrin are developed as soluble fiber
supplements for food products.
• It is also used as thickening agents in food
• They are polymers of D – glucose
• They are synthesised by the action of Leuconostoc mesenteroides.
• They are exocellular enzyme produced by the organisms which
bring about polymerisation of glucose moiety of sucrose molecule
• They differ from dextrins in structure.
• Contains α (1-4), α (1-6) and α (1-3) linkages.
• They are used as plasma expanders.
• They are also used as molecular sieves to separate proteins and other
• It is a heterogeneous polymer of D – fructose
• It has a low molecular weight than starch.
• It has got a linear chain with no branching.
• Occurs in the tubers of the Dehlia, in the roots of
Jerusalem artichoke, dandelion and in the bulbs of
onion and garlic.
• β(1-2) linked fructo furanoses
• Complete hydrolysis yields fructose
• Used for the evaluation of glomeular filtration rate.
• Used as a low glycemic index sweetner.
• It is a polymer of galactose units.
• It is obtained from the cell walls of some species of red
algae (Sphaerococcus Euchema) and species of Gelidium.
• When agar is dissolved in hot water and cooled, it becomes
• Used in microbiology, to make salt bridges and gel plugs
for use in electrochemistry.
• Used as a laxative, a thickener for soups, jellies, ice cream.
• Used as a clarifying agent in brewing and for sizing fabrics.
• They are high molecular weight carbohydrate polymers
containing more than one kind of monosaccharide.
• Chemically, they are formed mostly of repeated disaccharide
units that contains amino sugar and uronic acid.
• Some contain amino sugar and monosaccharide units without the
presence of uronic acid.
• Amino group is generally acetylated.
• Carbohydrate content more than 4% - mucoproteins.
• Carbohydrate content less than 4% - glycoproteins.
Acidic Sulphate free mucopolysaccharides
• Acidic polysaccharides are polysaccharides that contain
carboxyl groups, phosphate groups and/or sulphuric ester
• Example for acidic sulphate free mucopolysaccharides are
– Hyaluronic acid
• Composed of N – acetyl glucosamine and D – Glucuronic acid.
• On hydrolysis yields equimolecular quantities of D –
Glucosamine, D – Glucoronic acid and acetic acid.
• Occurrence – synovial fluid, ECM of loose connective tissue.
Serves as a lubricant and shock absorber.
• Hyaluronidase – an enzyme that catalyses the de polymerisation
of hyaluronic acid and by reducing its viscosity facilitates
diffusion of materials into tissue spaces.
• Clinically the enzyme is used to increase the efficiency of
absorption of solutions administered by clysis.
• It is another sulphate free acidic mucopolysaccharide.
• It is found in cornea and also in cranial cartilages.
• Composed of N – acetyl galactosamine and D – Glucoronic
Acidic sulphate containing mucopolysaccharides
They are mainly of four types:
1) Chondroitin sulphate
2) Keratan sulphate
4) Heparitin sulphate
• It is a sulphated glycosaminoglycan composed of a chain of alternating
sugars (N –acetylgalactosamine and glucuronic acid). It is usually
found attached to protein as part of proteoglycan.
• It is a principle mucopolysaccharide in ground substance of
mammalian tissues and cartilages.
• Four chondroitin sulphate are isolated which are chondroitin sulphate
A, B, C and D.
• Chondroitin sulphate A
Consists of repeating units of N – acetyl – D – galactosamine and D –
Glucuronic acid. N – acetylgalactosamine is esterified with sulphate in
position 4 of galactosamine.
It is present in cartilages, bone and cornea.
• Chondroitin sulphate B
It is present in skin, cardiac valve and tendon
It has L – iduronic acid in place of glucuronic acid which is
found in other chondroitin sulphate
L – iduronic acid is an epimer of D – Glucuronic acid
It consists of repeating units of L – iduronic acid and N – acetyl
galactosamine at C4 sulphate moiety is present.
It has weak anticoagulant property
Sometimes it is found in the skin and hence it is known as
• Chondroitin sulphate C
It is found in cartilage and tendon.
Structure is similar to chondroitin sulphate A except that
sulphate group is present at position 6 of the galactosamine
molecule instead of position 4
• Chondroitin Sulphate D
It is isolated from the cartilage of shark
It resembles in structure to chondroitin sulphate C, except
that it has second sulphate attached to carbon 2 or 3 of
• It is a sulphate containing acid mucopolysaccharide
• It is found in coastal cartilage, cornea, aorta, nucleous
• It consists of repeating disaccharide units of N – acetyl – D
– glucosamine 6 – sulphate and galactose.
• They are no uronic acids in this molecule.
• It is an anticoagulant present in liver which is produced by the mast
cells present in liver.
• It is found in lungs, thymus, spleen, walls of large arteries, skin, blood
• It is a polymer of repeating disaccharide unit of D – Glucosamine and
either of the two uronic acid (D – Glucuronic acid and L – iduronic
• In fully formed heparin molecule 90% or more of uronic acid residues
are L – iduronic acid
• It is found in Pneumococci capsule.
• It acts as blood group substances. Four monosaccharides:
Galactose, Fucose, Galactosamine (acetylated) and
glucosamine (acetylated) are present in all types of blood
• It is also found in egg protein known as ovalbumin.
• Glycoproteins are proteins that contain oligosaccharide chains or
glycans which are covalently attached to polypeptide side chains.
• Almost all the plasma proteins of humans with the exception of
albumin are glycoproteins.
• Glycosylation (enzymic attachment of sugars) is the most
frequent post – translational modification of proteins.
• Non – enzymic attachment of sugars to proteins can also occur
and it is referred to as glycation.
Difference between glycoproteins and proteoglycans
Features Glycoproteins Proteoglycans
Composition Carbohydrates less than protein (1
Carbohydrates more than
Smaller (2 – 10 sugar residues) Very long
No (Very heterogeneous) Yes
• Eight sugars are commonly found in the
oligosaccharide chains of glycoproteins
– Galactose (Gal)
– Glucose (Glc)
– Xylose (Xyl)
– Mannose (Man)
– Fucose (Fuc)
– N – acetylglucosamine (GlcNAc)
– N – acetylgalactosamine (GalNAc)
– N – acetyl neuraminic acid (NeuAc)
• The percentage of carbohydrate in glycoproteins is highly variable
– Some glycoproteins such as IgG contains low amounts (4%) of
carbohydrate by weight, while glycophorin, the human red cell
membrance glycoprotein contains 60% of carbohydrate.
• The carbohydrate can be distributed fairly evenly along the
polypeptide chain or concentrated in defined regions.
Functions of oligosaccharide chains of glycoproteins
Stabilisation of protein structure
Prevent degradation of the protein by proteinases
Increase in the polarity and solubility of a protein
Control of protein half life in blood
Important determinant in receptor – ligand binding
It may affect the sites of metastasis selected by cancer cells.
Functions of glycoproteins
They are found throughout matrices and act as receptors on cell
surfaces that bring other cells and proteins (collagen) together giving
strength and support to a matrix
In certain bacteria, a slime layer that surrounds the outermost
components of cell walls are made up of glycoproteins of high
In nerve tissue, glycoproteins are abundant in grey matter and appear
to be associated with synaptosomes, axons and microsomes.
Glycoprotein enzymes are of three types which include
oxidoreductases, transferases and hydrolases.
There are many glycoproteins that functions as hormones such as
human chorionic gonadotropin (HCG) which is present in human
pregnancy urine, thyroid stimulating hormone (TSH).
Another example is erythroprotein which regulates erythrocyte
Glycoprtoeins serve to adhere cells to cells and cells to substratum. Cell
– cell adhesion is the basis for the development of functional tissues in
In different domains of the body, the different glycoproteins act to unite
cells, for example nerve cells recognize and bind to one another via the
glycoprotein N –CAM (nerve cell adhesion molecule).
N – CAM is also found on muscle cells indicating a role in the
formation of myoneural junctions.
Glycoproteins found on the surface of spermatozoa appear to increase a
sperm cell’s attraction for the egg by altering the electrophoretic mobility of
the plasma membrane.
Hen ovalbumin is a glycoprotein found in egg white that serves as a food
storage unit for the embryo.
The zona pellucida is an envelope made of glycoprotein that surrounds the
egg and prevents polyspermy from occuring after the first sperm cell has
penetrated the egg’s plasma membrane.
Human sweat glands secrete glycoproteins which protect the skin from
other excretory products that could harm the skin.
Mucins are also found on the outer body surfaces of fish to protect the skin.
Not only does mucin serve the function of protection, but it also acts as a
Mucins form a highly viscous gel that protects epithelium from chemical,
physical and microbial disturbances. Examples of mucin sites are the human
digestive tract, urinary tract and respiratory tracts.
Types of glycoproteins
Based on the nature of the linkage between their polypeptide chains and
their oligosaccharide chains, glycoproteins can be divided into three major
O – linked
N – linked
GPI – anchored
1. N – linked glycans
They are found in the ovalbumin and the immunoglobulins.
Another use of N – linked oligosaccharides is in intracellular targeting in
Amide nitrogen of aspargine and N – acetylglucosamine (GlcNAcAsn)
Anomeric carbon of NAG – attached to amide nitrogen of an Asn
It is 5 times more abundant than O – linked
2. O – linked glycans
Hydroxyl side chain of serine or threonine and a sugar such as N –
acetylgalactosamine (GalNAc – Ser[Thr])
Anomeric carbon of NAG – attached to O of serine or threonine.
Mucins which are found extensively in salivary secretions, contain many
short O – linked glycans.
Increase the viscosity of the fluids in which they are dissolved.
3. GPI – anchored or GPI – linked (Glycosylphosphatidylinositol –
Carboxyl terminal amino acid of a protein via a phosphoryl – ethanolamine
moiety joined to an oligosaccharide (glycan), which in turn is linked via
glucosamine to phosphatidylinositol.
The GPI anchor may allow greatly enhanced mobility of a protein in the
Some GPI anchors may connect with signal transduction pathways.
Some examples include Acetylcholinesterase, Alkaline phosphatase