Basics of carbohydrates
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The document discusses the basics of carbohydrates including their definition, classification, structure, and qualitative tests for identification. It covers that carbohydrates have the general formula Cn(H2O)n, are classified into monosaccharides, disaccharides, oligosaccharides, and polysaccharides, and common qualitative tests include Molisch's test, iodine test, Benedict's test, and Fehling's test.
Basics of carbohydrates
- 2. Introduction: •They have a general formula – Cn(H2O)n , n>3. •They contain 3 main elements ; carbon ,hydrogen and oxygen. Definition: “carbohydrates are polyhydroxy aldehydes or ketones and their derivatives.”
- 4. Classification of Carbohydrates: 1) Monosaccharides- cannot be broken down into smaller units by hydrolysis. Sometimes called simple sugars. a) Trioses – glyceraldehyde b) Tetroses- Erythrose c) Pentoses- ribose d) hexoses- glucose 2) Disaccharides- can be broken down (hydrolyzed) into two monosaccharide units. Ex -lactose, maltose etc, 3) Oligosaccharides- can be broken into three to six monosaccharide units. Ex- Raffinose 4) Polysaccharides- composed of 7 or more mono-saccharide units . a) Homo polysaccharides: Ex- Starch, Glycogen etc,. b) Hetero polysaccharides: Ex- hyaluronic acid, heparin etc,
- 5. Structure of monosaccharide’s, disaccharides and polysaccharides:
- 6. Reducing and non-reducing sugars: •Reducing sugars: - a sugar which has a free aldehyde group or a free ketone groupthat can reduce benedict’s reagent. Ex.-glucose, lactose, maltose etc, •Non-Reducing sugars: - a sugar which do not have a free aldehyde group or a free ketone group and thus, cannot reduce benedict’s reagent. Ex.- Sucrose.
- 7. Mutarotation: Mutarotation is the change in the optical rotation because of the change in the equilibrium between α and β anomeric forms of glucose.
- 8. Disorders of carbohydrate metabolism: •Glycogen storage disorders: Glycogen storage disease (GSD, also glycogenosis) is the result of defects in glycogen-synthesis or breakdown related enzymes within muscles, liver, and other cell types. It can be genetic or acquired. Example- type-1disorder (Gierke’s disease)- due to defect of glucose- 6-phosphatase enzyme, cori’s disease etc,.
- 9. Qualitative tests or identification tests for carbohydrates: 1)Molisch’s test: -test for carbohydrates. Few drops Molisch reagent+ 2ml sample+ conc.H2SO4- along sides of test tube: carbohydrates on dehydration by sulfuric acid produce furfural which then condenses with the -naphthol resulting in a red or purple-colored ring at the junction of 2 liquids. 2) Iodine test: -test for polysaccharides. 2ml sample+iodine solution drop wise- Iodine solution based on adsorption reacts with starch producing a blue-black color.
- 10. 3) Barfoed’s test: -test for monosaccharides. 2ml sample+5ml reagent+ boil 2min- In Barfoed’s reagent, cupric acetate in acetic acid, is balanced so that is can only be reduced by monosaccharides forming brick-red cuprous oxide precipitate. 4) Seliwanoff’s test: -test for ketoses. 2ml sample + 5ml reagent+ boil 2min- When heated with reagent, ketoses are more rapidly dehydrated than aldoses, a red color appears.
- 12. 5) Benedict’s test: -test for reducing sugars. 5ml Benedict's reagent +few drops sample- The reducing sugar here reduces the cupric ions in these test solutions to cuprous ions, which then forms a brick red copper oxide precipitate. 6) Fehling’s test: -test for reducing sugars. 5ml Fehling’s reagent+ few drops sample- The reducing sugar here reduces the cupric ions in these test solutions to cuprous ions, which then forms a brick red copper oxide precipitate.
- 13. BENEDICT’S TEST:
- 14. 7) Osazone test: • microscopic test for crystalline structure of carbohydrates. •Osazones are formed when the sugars react with a compound known as phenylhydrazine hydrochloride at boiling point. •Osazone crystals have a characteristic shape nder the light microscope, ths help in identification of sugar type.
- 15. Osazone formation (microscopic view):