They are branched or unbranched polymers of monosaccharides jointed by glycosidic bond. Their general formula is (C6H10O5)n They are also called glycans polysaccharides are amorphous, tasteless and insoluble or only slightly soluble in water and can be easily hydrolysed to monosaccharide units.
# (1) Types of polysaccharides
On the basis of structure
(i) Homopolysaccharides : These are made by polymerisation of single kind of monosaccharides. e.g. starch, cellulose, glycogen, etc.
(ii) Heteropolysaccharide : These are made by condensation of two or more kinds of monosaccharides. e.g. chitin, pectin, etc.
# On the basis of functions
(i) Food storage polysaccharides : They serve as reserve food. e.g. starch and glycogen.
(ii) Structural polysaccharides : These take part in structural framework of cell wall e.g. chitin and cellulose.
# (2) Description of some polysaccharides
- (i) Glycogen : It is a branched polymer of glucose and contain 30,000 glucose units. It is also called animal starch. Their general formula is (C6H10O5)n .It is also found as storage product in blue green algae, slime moulds, fungi and bacteria. It is a non-reducing sugar and gives red colour with iodine. In glycogen, glucose molecule are linked by 1 – 4 glycosidic linkage in straight part and 1 – 6 linkage in the branching part glycogen has branch points about every 8-10 glucose units.
- (ii) Starch : Starch is formed in photosynthesis and function as energy storing substance. Generally found in the form of grains, which contain 20% water. It is found abundantly in rice, wheat, legumes, potato (oval and ecentric shaped), banana, etc. Starch is of two types. Straight chain polysaccharides known as amylose and branched chain as amylopectin. Both composed of D – glucose units jointed by linkage and linkage. It is insoluble in water and gives blue colour when treated with iodine. Amylose consists of 200 – 500 glucose units. It is stored inside chloroplast or spherical leucoplast and known as amyloplasts.
- (iii) Inulin : Also called “dahlia starch”(found in roots). It has unbranched chain of 30 – 35 fructose units linked by – 1 glycosidic linkage between 1 and 2 of carbon atom of D – fructose unit.
(iv) Cellulose : An important constituent of cell wall (20 – 40%), made up of unbranched chain of 6000 –D glucose units linked by 1 – 4 glycosidic linkage. It is fibrous, rigid and insoluble in water. Wood (20 – 50%) and cotton (90%) contain large amount of it. Rayon (artificial fibre) cellulose, nitrate (used as explosive) and carboxyl methyl cellulose (used as cosmetics and ice cream) are obtained by activity of “cellulase” enzyme. It doesn’t give any colour when treated with iodine.
- (v) Chitin : It is a polyglycol consisting of N-acetyl–D–glucosamine units connected with glycosidic linkage. Mostly it is found in hard exoskeleton of insects and crustaceans and some times in fungal cell wall. Second most abundant carbohydrate.
- (vi) Agar-Agar : It is a galactan, consisting of both D and L galactose and it is used to prepare bacterial cultures. It is also used as luxative and obtained from cell wall of red algae e.g. Gracilaria, Gelidium, etc.
- (vii) Pectin : It is a cell wall material in collenchyma tissue may also be found in fruit pulps, rind of citrus fruits etc. It is water soluble and can undergo sol - gel transformation. It contain arabinose, galactose and galacturonic acid.
- (viii) Neutral sugars : It is found associated with cellulose in cell wall. The common sugars in hemicellulose are D-xylose, L–arabinose, D-galactose, D-mannose and D-glucusonic acid. e.g. hemicellulose.
- (ix) Gum : It secreted by higher plants after injury or pathogenic attacks. It is viscous and seals the wound. It involves sugars like L-arabinose, D-galactose, D-glucusonic acid. e.g. gum arabic.
- (x) Mucopolysaccharides : These are gelatinous substance, containing amino sugars, uronic acid, etc. All slimy substances of plant are mucopolysaccharide. e.g. hyaluronic acid, vitreous humour, chondridine sulphate, heparin, husk of isabgul and mucilage of also.
- (xi) Glycoproteins : They include some plasmaprotein and blood group substances. They doesn’t contain uronic acid.
- (xii) Murein : It is a peptidoglycan, linked to short chains of peptides. It is constituent of cell wall of bacteria and blue green algae.
# (3) Properties of polysaccharides
(i) They are tasteless and colourless solids.
(ii) Insoluble in water, soluble in alcohol and more soluble in ether.
(iii) Can be easily hydrolyzed into their monosaccharide.
(iv) Their molecular weight is high.
(v) They do not diffuse through plasma membrane.
# (4) Functions
(i) Cellulose pectin and chitin are constituents in cell wall of higher plants but peptidoglycan in the cell wall of prokaryotes.
(ii) They are reserve food material.
(iii) They form protective covering.
(iv) They can be used as culture medium.
(v) Being insoluble they do no exert osmotic or chemical influence in the cell.
(vi) Fibres are obtained used in making cloth and rope.
(vii) Nitrocellulose and trinitrate cellulose (gun-cotton) used as explosive.
They are branched or unbranched polymers of monosaccharides jointed by glycosidic bond. Their general formula is (C6H10O5)n They are also called glycans polysaccharides are amorphous, tasteless and insoluble or only slightly soluble in water and can be easily hydrolysed to monosaccharide units.
# (1) Types of polysaccharides
On the basis of structure
(i) Homopolysaccharides : These are made by polymerisation of single kind of monosaccharides. e.g. starch, cellulose, glycogen, etc.
(ii) Heteropolysaccharide : These are made by condensation of two or more kinds of monosaccharides. e.g. chitin, pectin, etc.
# On the basis of functions
(i) Food storage polysaccharides : They serve as reserve food. e.g. starch and glycogen.
(ii) Structural polysaccharides : These take part in structural framework of cell wall e.g. chitin and cellulose.
# (2) Description of some polysaccharides
- (i) Glycogen : It is a branched polymer of glucose and contain 30,000 glucose units. It is also called animal starch. Their general formula is (C6H10O5)n .It is also found as storage product in blue green algae, slime moulds, fungi and bacteria. It is a non-reducing sugar and gives red colour with iodine. In glycogen, glucose molecule are linked by 1 – 4 glycosidic linkage in straight part and 1 – 6 linkage in the branching part glycogen has branch points about every 8-10 glucose units.
- (ii) Starch : Starch is formed in photosynthesis and function as energy storing substance. Generally found in the form of grains, which contain 20% water. It is found abundantly in rice, wheat, legumes, potato (oval and ecentric shaped), banana, etc. Starch is of two types. Straight chain polysaccharides known as amylose and branched chain as amylopectin. Both composed of D – glucose units jointed by linkage and linkage. It is insoluble in water and gives blue colour when treated with iodine. Amylose consists of 200 – 500 glucose units. It is stored inside chloroplast or spherical leucoplast and known as amyloplasts.
- (iii) Inulin : Also called “dahlia starch”(found in roots). It has unbranched chain of 30 – 35 fructose units linked by – 1 glycosidic linkage between 1 and 2 of carbon atom of D – fructose unit.
(iv) Cellulose : An important constituent of cell wall (20 – 40%), made up of unbranched chain of 6000 –D glucose units linked by 1 – 4 glycosidic linkage. It is fibrous, rigid and insoluble in water. Wood (20 – 50%) and cotton (90%) contain large amount of it. Rayon (artificial fibre) cellulose, nitrate (used as explosive) and carboxyl methyl cellulose (used as cosmetics and ice cream) are obtained by activity of “cellulase” enzyme. It doesn’t give any colour when treated with iodine.
- (v) Chitin : It is a polyglycol consisting of N-acetyl–D–glucosamine units connected with glycosidic linkage. Mostly it is found in hard exoskeleton of insects and crustaceans and some times in fungal cell wall. Second most abundant carbohydrate.
- (vi) Agar-Agar : It is a galactan, consisting of both D and L galactose and it is used to prepare bacterial cultures. It is also used as luxative and obtained from cell wall of red algae e.g. Gracilaria, Gelidium, etc.
- (vii) Pectin : It is a cell wall material in collenchyma tissue may also be found in fruit pulps, rind of citrus fruits etc. It is water soluble and can undergo sol - gel transformation. It contain arabinose, galactose and galacturonic acid.
- (viii) Neutral sugars : It is found associated with cellulose in cell wall. The common sugars in hemicellulose are D-xylose, L–arabinose, D-galactose, D-mannose and D-glucusonic acid. e.g. hemicellulose.
- (ix) Gum : It secreted by higher plants after injury or pathogenic attacks. It is viscous and seals the wound. It involves sugars like L-arabinose, D-galactose, D-glucusonic acid. e.g. gum arabic.
- (x) Mucopolysaccharides : These are gelatinous substance, containing amino sugars, uronic acid, etc. All slimy substances of plant are mucopolysaccharide. e.g. hyaluronic acid, vitreous humour, chondridine sulphate, heparin, husk of isabgul and mucilage of also.
- (xi) Glycoproteins : They include some plasmaprotein and blood group substances. They doesn’t contain uronic acid.
- (xii) Murein : It is a peptidoglycan, linked to short chains of peptides. It is constituent of cell wall of bacteria and blue green algae.
# (3) Properties of polysaccharides
(i) They are tasteless and colourless solids.
(ii) Insoluble in water, soluble in alcohol and more soluble in ether.
(iii) Can be easily hydrolyzed into their monosaccharide.
(iv) Their molecular weight is high.
(v) They do not diffuse through plasma membrane.
# (4) Functions
(i) Cellulose pectin and chitin are constituents in cell wall of higher plants but peptidoglycan in the cell wall of prokaryotes.
(ii) They are reserve food material.
(iii) They form protective covering.
(iv) They can be used as culture medium.
(v) Being insoluble they do no exert osmotic or chemical influence in the cell.
(vi) Fibres are obtained used in making cloth and rope.
(vii) Nitrocellulose and trinitrate cellulose (gun-cotton) used as explosive.