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Carbohydrates o They are polyhydroxy aldehydes and ketones . o Carbohydrates are compounds of C, H, and O. Major Categories of Carbohydrates 1. Monosaccharide 2. Disaccharide 3. Polysaccharide Monosaccharide o The simplest form of sugars. o Cannot be changed to simpler sugars upon hydrolysis. o Classified according to: 1. The number of carbon atoms present in the molecule. 2. Whether they contain an aldehyde or ketone. Monosaccharide # of Carbons Class 3 triose 4 tetrose 5 pentose 6 hexose Monosaccharide o The prefixes ‘aldo-’ and ‘keto-’ are used depending on whether the monosaccharide has an aldehyde or ketone group. Monosaccharide o Monosaccharide are called reducing sugars because they act as reducing agents and are easily oxidized to carboxylic acids. Glucose o White crystalline solid that is soluble in most organic liquids o Is an aldohexoses o Found along with fructose in many fruite juices o Most important monosaccharide o Found in the blood stream and in tissue fluids o Requires no digestion Glucose Forms of Glucose o α and β forms: - When the OH on C number1 is downward the form is α. - When the OH on C number 1 is upward the form is β. o D and L forms: CH 2 OH H C OH C CH 2OH O H H H OH H C C H OH α –D glucose C C OH OH Mirror O C H C H C H OH C H OH OH β-L glucose Fructose o Is a ketohexose o Occurs naturally in juices and honey o The most soluble and sweetest of all sugars α- D Fructose β-D Fructose Disaccharide Maltose hydrolysis Glucose + Glucose Sucrose Lactose hydrolysis Glucose + Fructose Glucose + Galactose hydrolysis o Sucrose is soluble in water, maltose is fairly soluble, and lactose is slightly soluble. o They are too large to pass through cell membrane. o Formed by the combination of tow monosaccharide’s. o Bond between tow monosaccharide’s is called glycosidic linkage. o Maltose o Present in germinating grain o Produced by hydrolysis of starch o Reducing sugar o Sucrose: o Is the ordinary table sugar used in home. o Non-reducing sugar. Polysaccharide o Comparison of polysaccharide with mono and disaccharide Property Mono and Di Poly Molecular mass Low Very high Taste Sweet Tasteless Solubility in water Soluble Insoluble Size of particle Mono only pass through the membrane Do not pass Reducing property Reducing except for sucrose Non reducing Polysaccharide o Starch is the storage form of glucose in plants. o Glycogen is the storage form of glucose in animals where it is found in liver and muscles. o Cellulose is the primary structural component of plants. Chemical properties 1. Molisch test - General test for carbohydrates - Shows positive result for all carbohydrates To the left negative result, to the right positive result 2. Fehling’s test - Fehling is copper (II) complex ion - When reducing agent reacts with oxidizing agent (Cu2+) a red-orange ppt of copper(I) oxide is formed R CHO + Cu2+ deep blue color R COOH + Cu2O + H2O red-orange ppt 3. Barfoed’s test - To distinguish mono from disaccharide on the bases of different rate of reaction. - Mono reacts much faster. - +ve result prick red 4. Seliwanoff’s test - To distinguish ketoses (fructose) from aldoses (glucose) on the bases of different rates of reation - Ketohexoses reacts much faster. - +ve resultred 5. Iodine test - To distinguish starch from other polysaccharide. - +ve result blue coloration