Polysaccharides

Polysaccharides are polymers of D-glucose

Important polysaccharides are: Starch (Amylose and Amylopectin) Glycogen Cellulose Chitin

O

OH

CH2OH

OH

OH

OH

D-Glucose

Polysaccharides

Insoluble store of glucose in plants

formed from two glucose polymers:

(Amylose, Amylopectin)

Starch

Starch (Amylose, Amylopectin)

Amylose is a continuous chain of glucose

molecules linked by -1,4 glycosidic bonds.

Amylopectin is a branched chain of glucose

molecules linked by -1,4- and -1,6-glycosidic

bonds.

Amylose

-glucose 1,4 glycosidic bonds Spiral structure

Amylopectin

-glucose 1,4 and some 1,6

glycosidic bonds Branched structure

Starch

Structures of Amylose and Amylopectin

Glycogen

Glycogen is similar to amylopectin, but more highly branched.

Insoluble compact store of glucose in animals

-glucose units 1,4 and 1,6 glycosidic bonds Branched structure

GLYCOGEN• It is the main reserve food in animals and is often called animal starch.• Glycogen is stored in the liver and muscles of animals

Structure:

Glucose polymer, similar to amylopectin,but even more highly branched more α(16) branches.

α - (1 -> 4) linkage and α - (1 -> 6) linkag 1 : 12Uses:

The highly branched structure permits rapid glucose release from glycogen stores, e.g., in muscle during exercise. The many branched ends provide a quick means of putting glucose into the blood. The ability to rapidly mobilize glucose is more essential to animals than to plants.

Animals store glycogen in the liver (about a one-day supply in humans) and use it to maintain fairly constant blood sugar levels between meals

StarchesGlycogen

more branching

Sta

rch

/G

lycog

en

Cellulose

Structural polysaccharide in plants

-glucose with -1,4 glycosidic bonds

Cellu

los

e

Cellu

los

e

Cellulose Cellulose is the major structural polysaccharide of

plants. It is a long thread like molecule.• Cellulose is the main constituent of cell walls of

plants.• The role of cellulose is to impart strength and rigidity

to plant cell walls, which can withstand high hydrostatic pressure gradients.

Cellulose is a polymer of glucose molecules linked by -1,4 glycosidic bonds.

Enzymes in saliva (e.g. salivary amylase) can hydrolyze -1,4 glycosidic bonds in starch, but not -1,4 glycosidic bonds in cellulose.

Cellulose

Most organisms cannot digest (hydrolyze) cellulose

Organisms that can digest cellulose include the

microorganisms living the gastrointestinal tract of

many organisms typified especially by cows and

termites and many fungi (i.e., the things that “eat”

the wood of fallen trees)

Chitin

Chitin is another example of a structural

carbohydrate.

Chitin is found in the exoskeletons of insects and

spiders.

Chitin is also found in the cell walls of fungi.

Chitin is leathery in pure form but is hardened in

most uses via the deposition of calcium carbonate.

Ch

iti

n

Ch

iti

n

Some Familiar and Important Complex Carbohydrates

(a)The Polymer Amylose is a Major Component of Starch and is made Up of Alpha-D-Glucose Monomers.

(b) The Polymer Cellulose, which Consists of Beta-D-Glucose Monomers

Polysaccharides

• Glucose is the monosaccharides of the following polysaccharides with different linkages and branches – a(1,4), starch (more branch)– a(1,4), glycogen (less branch) – a(1,6), dextran (chromatography resins)– b(1,4), cellulose (cell walls of all plants)– b(1,4), Chitin similar to cellulose, but C2-OH is replaced

by –NHCOCH3 (found in exoskeletons of crustaceans, insects, spiders)

Amylose

Polymer with α-1,4 bonds

α-1,4 bonds

OOH

OH

CH2OH

O

O

OH

OH

CH2OH

O

O

OH

OH

CH2OH

O

O O

OH

OH

CH2OH

O

Amylopectin

Polymer with α-1,4 and α-1,6 bonds branches

α-1,6 bond

α-1,4 bonds

OOH

OH

CH2OH

O

O

OH

OH

CH2OH

O

O

OH

OH

CH2

O

O O

OH

OH

CH2OH

O

OOH

OH

CH2OH

O

O

OH

OH

CH2OH

O

O

OH

OH

CH2OH

O

O

Cellulose

Polymer with ß-1,4 bonds

ß-1,4 bondsO

O

OH

OH

CH2OH

O

O

OH

OH

CH2OH

O

O

OH

OH

CH2OH

O