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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
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
