Polysaccharides

Polysaccharides Polysaccharides are polymers of D-glucose Important polysaccharides are: Starch (Amylose and Amylopectin) Glycogen Cellulose Chitin D-Glucose

Starch Insoluble store of glucose in plants formed from two glucose polymers: (Amylose, Amylopectin)

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.

Starch Amylose Amylopectin -glucose 1,4 glycosidic bonds Spiral structure Amylopectin -glucose 1,4 and some 1,6 glycosidic bonds Branched structure

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 Glycogen is stored in the liver and muscles of animals 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(16) branches. α - (1 -> 4) linkage and α - (1 -> 6) linkag 1 : 12 Uses: 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

Starches Glycogen more branching

Starch/Glycogen

Cellulose Structural polysaccharide in plants -glucose with -1,4 glycosidic bonds

Cellulose

Cellulose

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.

Chitin

Chitin

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

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

Cellulose Polymer with ß-1,4 bonds ß-1,4 bonds