Polysaccharides are carbohydrate molecules composed of monosaccharide units linked by glycosidic bonds. They can be classified as homopolysaccharides containing a single monosaccharide unit or heteropolysaccharides containing multiple types of units. Common homopolysaccharides include starch, glycogen, and cellulose which serve storage and structural functions. Heteropolysaccharides like hyaluronic acid and chondroitin sulfate provide extracellular support and are components of connective tissues.

1. POLYSACCHARIDES
Fyna Sebastian
Assistant Professor
Department Of Biotechnology
St. Mary’s College, Thrissur
Kerala

2. Polysaccharides
 Polysaccharides, which are also known as glycans, consist of
monosaccharides linked together by glycosidic bonds.
 Polysaccharides can be broadly classified into two classes:
 Homopolysaccharides
 Heteropolysaccharides
 Homopolysaccharides consist of one type of monosaccharide
units. Ex: Cellulose, starch, glycogen.
 Heteropolysaccharides cconsist of two or more types of
monosaccharide units. Ex: Hyaluronic acid and they provide
extracellular support for organisms.
Biomolecules, Fyna Sebastian, St. Mary’s College, Thrissur

3. Functions of Polysaccharides
 Storage polysaccharides: Starch and glycogen stored in the
liver and muscles to be converted to energy later for body
functions.
 Starch plants
 Glycogen animals.
 Structural polysaccharides: Cellulose found in the cell walls
of plants and chitin found in exoskeleton of vertebrates like
insects
Biomolecules, Fyna Sebastian, St. Mary’s College, Thrissur

4. Homopolysaccharides
1. Starch
 It is the storage polysaccharide found in plant cells
 Exists in two forms: amylose and amylopectin
 Amylose is the helical form of starch comprised only of D-
glucose units by α (1 4) linkages
 Amylopectin composed of α (1 6) glycosidic bonds at
the branching points and α (1 4) bonds present
everywhere else
Biomolecules, Fyna Sebastian, St. Mary’s College, Thrissur

5. Figure 1:a) Amylose b) Amylopectin
a) b)
Biomolecules, Fyna Sebastian, St. Mary’s College, Thrissur

6. 2.Glycogen
 Found in animals to store energy
 Composed D-glucose as repeating unit with α (1 4)
glycosidic bonds and α (1 6) bonds present at
branching points about every tenth monomer
 It is mainly produced by the liver and muscles
 It can also be made during a process called glycogenesis.
Biomolecules, Fyna Sebastian, St. Mary’s College, Thrissur

7. Figure 2: Glycogen
Biomolecules, Fyna Sebastian, St. Mary’s College, Thrissur

8. 3.Cellulose
 Structural polysaccharide that is found in the cell wall of
plants
 Cellulose is said to be the most abundant organic molecule
on earth
 Wood, paper, and cotton are common forms of cellulose
 Composed of β-D-glucose units linked by β(1 4)
glycosidic bonds
 Cannot be digested
 When consumed, it acts as a dietary fibre – helps to
decrease the absorption of cholesterol from intestine
Biomolecules, Fyna Sebastian, St. Mary’s College, Thrissur

9. Figure 3: Cellulose
Biomolecules, Fyna Sebastian, St. Mary’s College, Thrissur

10. Hetero polysaccharides
Mucopolysaccharides
 Commonly known as Glycosaminoglycans (GAG)
 Contain acetylated amino groups and carboxylic groups –
acidity of molecules.
 They form important components of connective tissues
and are found in collagen and elastin.
 Important mucopolysaccarides – hyaluronic acid,
chondroitin-sulphate, heparin etc.
Biomolecules, Fyna Sebastian, St. Mary’s College, Thrissur

11. 1.Hyaluronic Acid
 Important GAG
 Acts as a lubricant in the synovial fluid of joints and vitreous
humor of eyes
 Composed of D-glucuronic acid and N-acetyl D-glucosamine
units linked by β(1 3) bonds.
 Hyaluronidase enzyme break bonds between hyaluronic acid
Biomolecules, Fyna Sebastian, St. Mary’s College, Thrissur

12. D-glucuronic acid N-acetyl D-glucosamine
Figure 4 : Hyaluronic acid
Biomolecules, Fyna Sebastian, St. Mary’s College, Thrissur

13. 2.Chondroitin Sulfate
 It contributes to tensile strength and elasticity of cartilages,
tendons, ligaments, and walls of the aorta.
D-Glucuronic acid N-acetyl-D-Galactosamine
Figure 5: Chondroitin sulfate
Biomolecules, Fyna Sebastian, St. Mary’s College, Thrissur

14. 3.Dermatan sulfate
 It is found mainly in the skin, heart and lungs
 It may be related to coagulation and vascular diseases
and other conditions.
L-Iduronic acid N-Acetyl-D-Galactosamine
Figure 6: Dermatan sulfate
Biomolecules, Fyna Sebastian, St. Mary’s College, Thrissur

15. 4.Keratan sulfate
 Present in the cornea, cartilage bone and a variety of
other structures as nails and hair.
 Only GAG with no uronic acid
D-galactosamine N-acetylglucosamine
Figure 7: Keratan sulfate
Biomolecules, Fyna Sebastian, St. Mary’s College, Thrissur

16. 5.Heparin
 present as an anticoagulant in the blood.
L-Iduronic acid D-Glucosamine
Figure 8: Heparin
Biomolecules, Fyna Sebastian, St. Mary’s College, Thrissur

17. Glycoprotein
 any of a class of proteins which are attached to
carbohydrate groups.
 Also called as mucoprotein
 Perform various functions
 Enzymes
 Hormones
 Transport proteins
 Structural protein
Biomolecules, Fyna Sebastian, St. Mary’s College, Thrissur

18. References
18
 Lehninger –Principles of Biochemistry 6th edition
 U Satyanarayana – Biochemistry 3rd edition
 https://usmle.biochemistryformedics.com
 https://quizlet.com/31134761/biochemistry-glycosaminoglycans-flash-
cards/