Polysaccharides

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/