Dr Praveen Kumar Agrawal is teaching live on Unacademy Plus
COURSE BIOMOLECULES Lesson Oligosaccharides (Disaccharides) Dr. Praveen Kumar Agrawal
Oligosaccharides Oligosaccharides (Gr. Oligo - few, saccharides sugar), are the compounds which are formed of 2 to 10 monosaccharides. During the synthesis of oligosaccharides, carbonyl group of one monosaccharide and alcoholic group of another monosaccharide condense, together, forming a bond, called glycosidic bond with the loss of a water molecule. This synthesis is called dehydration synthesis. Compounds containing glycosidic bonds are called glycosides.
CH2OH CH2OH CH2 OH CH2 OH OH +HO OH OH H20 OH OH OH OH OH OH OH OH Glucose Glucose Maltose Glycosidic bond
Properties of oligosaccharides . Oligosaccharides are sweeter in taste. . These are crystalline solids. . Disaccharides are also reducing sugar but sucrose is an exception (as it has no free ketone or aldehyde group). Sucrose, therefore can not reduce Cu2+ to Cu+. But if it is hydrolysed to glucose and fructose, the mixture can give positive Benedicts test. .Physiologically important disaccharides are sucrose, lactose and maltose. .1. Sucrose It is also called cane sugar or table sugar or invert sugar. Sucrose is prevalent in sugar cane and sugar beets. It is composed of glucose and fructose, joined through an alpha -(1, 2) b -glycosidic bond 2. Maltose I It is commonly called malt sugar and it is formed by . two molecules of glucose. I It is the simplest oligosaccharide. 3. Lactose It is mainly found in milk of human being and cow. . Hence, it is also called milk sugar. . It is formed by one molecule of glucose and one of galactose. It is the least sweet sugar.
Oligosaccharides Monosaccharides forming glycosidic bond Sucrose Maltose Lactose Raffinose Stachyose Barbascose Glucose Fructose Glucose Glucose Glucose Galactose Glucose Fructose + Galactose Glucose Fructose +Galactose + Galactose Glucose Glucose Fructose Galactose Galactose