Polysaccharides are complex biomacromolecules made of monosaccharide units linked by glycosidic bonds, classified into structural and storage types. Key examples include cellulose, a structural polysaccharide in plant cell walls, and starch, a storage polysaccharide in plants. Their primary functions are to provide structural support, store energy, and facilitate cellular communication.

1. Polysaccharides
Presented by:
Jasmine Juliet
Biochemistry, ACRI, Madurai.

2. Polysaccharides - Introduction
 Polysaccharides are complex biomacromolecules.
 Polysaccharides or polycarbohydrates, are the most
abundant carbohydrate found in food.
 They are long chain polymeric carbohydrates.

3. Polysaccharides - Structure
 Polysaccharides are composed of monosaccharide units bound together
by glycosidic linkages.
 They are either linear or branched in structure.
 Polysaccharides may also be classified based on their function:
(i) Structural polysaccharides are usually present in the cell walls
and give shape and rigidity to the cells. Eg. Cellulose, hemicelluloses
(ii) Storage polysaccharides act as reserve food material. Eg. Starch,
glycogen

4. Polysaccharides - Structure
 Polysaccharides may be sub-classified into two types based on
the composition of monosaccharide units present.
 Homopolysaccharides are made up of a single type of
monosaccharide. Eg: starch, glycogen, cellulose, inulin.
 Heteropolysaccharides are made up of more than one type
of monosaccharides. Eg: Hemicelluloses, arabinogalactan

5. Polysaccharide - Starch
 Starch is a storage polysaccharide in plant cells.
 It is a homopolymer of α-D-glucose units.
 Starch has two main constituents.
(i) Amylose (15-20%) Linear polysaccharides
(ii) Amylopectin(80-85%) branched polysaccharides

7. Polysaccharide - Cellulose
 Cellulose is an example of a structural polysaccharide.
 It is used in the cell walls of plants and other organisms, and
is said to be the most abundant organic molecule.
 Cellulose is formed when β-glucose molecules are joined to
form a polymer.
 It is a straight chain polymer.
 Furthermore, due to the hydrogen bonds between molecules it
can form very rigid fibers.

10. Polysaccharide - Chitin
 Chitin is a structural polysaccharide found in the
exoskeleton of insects and crustaceans and in the cell
walls of fungi.
 It consists of N-acetyl-D-glucosamine units joined by
β-1,4 glycosidic linkages.
 Like cellulose it consists of parellel chains of molecules
held together by hydrogen bonds.

11. Chitin

12. Polysaccharide - Functions
 The three main functions of polysaccharides are:
(i) providing structural support,
(ii) storing energy, and
(iii) sending cellular communication signals.
 The carbohydrate structure largely determines its
function.

13. Review questions
A1. An example of heteropolysaccharide is
a)Amylose b) Hemicellulose c)Cellulose d) Amylopectin
A2. The repeating unit in chitin
a)Glucose b)Glucosamine c)Galactose d) N-acetyl glucosamine
A3. Glucose residues in amylose are linked by
a)α 1-4 b)β 1-4 c) α 1-6 d)β 1-6
A4.Which of the following is an example of homopolysaccharide
a)Starch b)Glycogen c)Cellulose d) All of these

14. Review questions
B1.Define polysaccharide?
Ans: Polysaccharides are composed of monosaccharide units
bound together by glycosidic linkages. Eg:Starch, cellulose.
C1. Describe the structure of starch?
Ans: Starch is a homopolymer of α-D-glucose units.Starch has
two main constituents (i) Amylose (15-20%) Linear
polysaccharides, (ii) Amylopectin(80-85%) branched
polysaccharides

15. Review questions
D1. Explain the classification of polysaccharides with
examples?