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Class 10 Oligosaccharides &Polysaccharides.ppt

  2. DISACCHARIDE • A disaccharide, also called a double sugar, is a molecule formed by two monosaccharides, or simple sugars. • Three common disaccharides are sucrose, maltose, and lactose. • Disaccharides are formed through dehydration reactions in which one water molecule is removed from the two monosaccharides. • They have 12 carbon atoms, and their chemical formula is C12H22O11. • Other, less common disaccharides include lactulose, trehalose, and cellobiose
  3. 1. Maltose • Maltose, also known as malt sugar, is formed from two glucose molecules. • Malt is formed when grains soften and grow in water, and it is a component of beer, starchy foods like cereal, pasta, and potatoes, and many sweetened processed foods. • Beverages : maltova, boost, horlicks etc. • In plants, maltose is formed when starch is broken down for food. It is used by germinating seeds in order to grow.
  4. 2. Cellobiose • Like maltose, cellobiose is also made up of two glucose molecules, but they are linked in yet another different way. • It is found when cellulose, the main component of plant cell walls, is hydrolyzed. • Cellobiose is used in bacteriology to perform chemical analyses.
  5. • Lactose • Lactose, or milk sugar, is made up of galactose and glucose. The milk of mammals is high in lactose and provides nutrients for infants. • Most mammals can only digest lactose as infants, and lose this ability as they mature.
  7. Sucrose : Sucrose, commonly known as table sugar in its refined form, is a disaccharide found in many plants. It is made up of the monosaccharides glucose and fructose. In the form of sugar, sucrose is a very important component of the human diet as a sweetener. SWEETNESS SCALE Sucrose - 100 Glucose - 70 Fructose - 170 Lactose - 30
  8. • Lactulose : Lactulose is formed from fructose and galactose. It can be used to treat constipation and liver disease • Trehalose : Trehalose is also made up of two glucose molecules like maltose, but the molecules are linked differently. It is found in certain plants, fungi, and animals like shrimp and insects. • The blood sugar of many insects, such as bees, grasshoppers, and butterflies, is made up of trehalose. They use it as an efficient storage molecule that provides rapid energy for flight when broken down.
  9. 3. Oligosaccharides • Oligosaccharides are carbohydrates that yield two to ten monosaccharide units on hydrolysis. • Raffinose and stachyose are two important oligosaccharides present in dried beans, peas and lentils, which yield three monosaccharide units on hydrolysis.
  10. STRUCTURE OF OLIGOSACCHARIDES • Raffinose, also called melitose, is a trisaccharide that is widely found in legumes and cruciferous vegetables, including beans, peas, cabbage, brussels sprouts, and broccoli. • It consists of galactose connected to sucrose via a α1→6 glycosidic linkage. • Humans cannot digest polysaccharides with this linkage and the trisaccharides are fermented in the large intestine by gas- producing bacteria.
  11. Fig.2.10 Structure of Raffinose
  12. Polysaccharides
  13. Polysaccharides • Polysaccharides are long carbohydrate chains that yield more than ten molecules of monosaccharide on hydrolysis. • Examples of polysaccharides are : glycogen, starch, cellulose and dextrin. • These are sometimes designated as hexosans or pentosans, depending upon the number of the monosaccharides they yield on hydrolysis. • They are called GLYCANS and NON-SUGARS
  14. STRUCTURE OF POLYSACCHARIDES 1. Starch • Starch is a polymer of glucose linked by α (1- 4) - glycosidic bond. (like maltose) • It yields only glucose on hydrolysis and hence is a homopolymer and is called a glucosan or glucan. • It is the most important food source of carbohydrate and is found in cereals, potatoes, legumes and other vegetables.
  15. • The two chief constituents of starch are amylose (15-20%) and amylopectin (80-85%). • Amylose has a non branching helical structure. • Amylopectin consists of branched chains composed of 24-30 glucose residues united by α(1-4) linkages in the chains and by α(1-6) linkages at the branch points • Rich sources of starch are : grains - wheat, rice, corn, oats, millets & barley legumes - peas, beans and lentils tubers - potatoes, yam and cassava
  16. Structure of Amylose
  17. Structure of Amylopectin
  18. 2.Glycogen • Glycogen is the storage polysaccharides of the animals. So often called - animal starch. • Its structure is similar to amylopectin, but it is highly branched. • It has chains of 12-14 -D-glucopyranose residues (in -[1-4] - glycosidic bond) with the branching by -(1-6 ) - glycosidic bonds • Skeletal muscle and the liver are the two important sites of glycogen storage.
  19. Structure of Glycogen
  20. 3. Dextrins • Dextrins are substances formed in the course of the hydrolytic break down of starch.
  21. 5. Cellulose • Cellulose is the chief constituent of the structure of plants. • It is insoluble and consists of D- glucopyranose units linked by  (1-4) glycosidic bonds (similar to cellobiose) to form long, straight chains strengthened by cross-linked hydrogen bonds.
  22. Structure of cellulose
  23. • Cellulose cannot be digested by many mammals, including humans, because of the absence of an enzyme that attacks the a linkages. • But, it is an important source of “bulk” in the diet. In the stomach of ruminants and other herbivores, there are microorganisms that can attack the linkage, making cellulose available as a major source of energy.
  24. 6. Chitin • Chitin is an important structural polysaccharide of invertebrates. • It is found in the exoskeletons of crustaceans and insects. • Structurally, chitin consists of : N - acetyl - D- glucosamine units joined by (1-4)-glycosidic bond.
  25. Structure Chitin
  26. 7. Pectins • Pectin occurs widespread in nature but is found especially in the pulp of citrus fruits, apples, beets and carrots. • The term ‘Pectin’ represents the substances which in the presence of sugar and proper acid concentration causes the formation of jellies. • Because of its ability to form a thick gel-like solution, pectin is used commercially in the preparation of jellies, jams, and marmalades. • Its thickening properties also make it useful in the confectionery, pharmaceutical, and textile industries
  27. CLASSIFICATION OF POLYSACCHARIDES • Homo glycan – Cellulose, starch, Chitin • Heteroglycan – Hemicellulose, Heparin Functional classification of polysaccharides • Nutrient / storage / digestible polysaccharide – Starch, Glycogen • Structural polysaccharide – Cellulose, Chitin
  28. • Pectin is combined with cellulose in the cell walls, from which it may be released by mild hydrolysis and converted into soluble pectin. • The combined, insoluble pectin is referred to as proptopectin. • When soluble pectin is boiled with dilute acid, it is slowly hydrolyzed to pectic acid and methyl alcohol.
  29. • Purified pectin accordingly is the methyl ester (many methyl groups per molecule) of pectic acid. • Pectic acid is a chain of at least 200 of (1-4) linked a-D galactopyranosyl uronic acid units. • Because of its ability to form a thick gel-like solution, pectin is used commercially in the preparation of jellies, jams, and marmalades. • Its thickening properties also make it useful in the confectionery, pharmaceutical, and textile industries
  30. • Pectin also has several health benefits in humans. • Included among these are its ability to reduce low density lipoprotein (LDL) levels, thereby lowering cholesterol levels, and its ability to slow the passage of food through the intestine, relieving diarrhea. • Pectin can also activate cell death pathways in cancer cells, indicating that pectin may play an important role in preventing certain types of cancer.