1. Lubert Stryer - Biochemistry Lehninger- Principles of Biochemistry Harper's -Illustrated Biochemistry References Text Book of Biochemistry with clinical

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  • Lubert Stryer - Biochemistry Lehninger- Principles of Biochemistry Harper's -Illustrated Biochemistry References Text Book of Biochemistry with clinical correlation, T M. Devlin
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  • Carbohydrates
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  • General characteristics Compounds composed of C, H, and O (CH 2 O) n when n = 5 then C 5 H 10 O 5 Not all carbohydrates have this empirical formula: Deoxysugars, Aminosugars Carbohydrates are the most abundant compounds found in nature (cellulose: 100 billion tons annually)
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  • General characteristics Most carbohydrates are found naturally in bound form rather than as simple sugars (Glycoconjugates) Polysaccharides (starch, cellulose, inulin, gums), Mucopolysaccharides (hyaluronic acid) Glycoproteins and proteoglycans (hormones, blood group substances, antibodies) Glycolipids (cerebrosides, gangliosides) Nucleic acids (Ribose and desoxyribose)
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  • Functions Sources of energy (Glucose, Fructose,..) Intermediates in the biosynthesis of other basic biochemical entities (Fats and proteins) Form structural tissues in plants and in microorganisms (cellulose, lignin, murein) Participate in cell-cell recognition, Cell-cell adhesion
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  • Classification of carbohydrates Monosaccharides (monoses or glycoses) Oligosaccharides (condensation products of two to ten monosaccharides) Di, tri, tetra, penta, up to 9 or 10 Most important are the disaccharides Polysaccharides or glycans ( more than 10 ) Homopolysaccharides Heteropolysaccharides
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  • Classification of Monosaccharides A. Number of carbons in chain Trioses (3C) tetroses (4C) pentoses (5C) hexoses (6C) heptoses (7C) B. Aldose or Ketose Aldoses (e.g., glucose) have an aldehyde group at one end Ketoses (e.g., fructose) have a keto group, usually at C2
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  • Aldose sugars
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  • Ketose sugars
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  • Sugars Exhibit Various Forms of Isomerism
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  • Aldose and Ketose isomers
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  • L and D Isomers Most of the monosaccharides occurring in mammals are D sugars, and the enzymes responsible for their metabolism are specific for this configuration. 1.L-arabinose 2.L-idoronic acid D Form: L form:
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  • Enantiomers
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  • Epimers Two sugars that differ only in the configuration around one carbon atom are called epimers ;
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  • Optical isomerism Asymmetric compounds rotate plane polarized light In general, a molecule with n chiral centers can have 2 n stereoisomers Of the 16 possible aldohexoses, eight are D forms and eight are L Most of the hexoses of living organisms are D isomers.
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  • POLARIMETRY Measurement of optical activity in chiral or asymmetric molecules using plane polarized light Measurement uses an instrument called a polarimeter (Lippich type) Rotation is either (+) dextrorotatory or (-) levorotatory
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  • polarimetry Magnitude of rotation depends upon: 1. The nature of the compound 2. The length of the tube (cell or sample container) usually expressed in decimeters (dm) 3. The wavelength of the light source employed; usually either sodium line at 589.3 nm or mercury vapor lamp at 546.1 nm 4. Temperature of sample 5. Concentration of analyte in grams per 100 ml
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  • D = Na + line T = temperature o C obs : observed rotation in degree (specify solvent) l = length of tube in decimeter c = concentration in grams/100ml [ ] = specific rotation Polarimetry
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  • Specific rotation of various carbohydrates at 20 o C D-glucose+52.7 D-fructose-92.4 D-galactose +80.2 L-arabinose+104.5 D-mannose+14.2 D-arabinose-105.0 D-xylose +18.8 Lactose+55.4 Sucrose+66.5 Maltose++130.4 Invert sugar-19.8 Dextrin+195
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  • In chemistry, a racemic mixture, or racemate, is one that has equal amounts of left- and right- handed enantiomers of a chiral molecule.chemistryamountsenantiomerschiral Racemic mixture A racemate is optically inactive A racemate is optically inactive A racemic mixture is denoted by the prefix ()- or dl- (for sugars the prefix DL - may be used), indicating an equal (1:1) mixture of dextro and levo isomers
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  • Tartaric acid It occurs naturally in many plants, particularly grapes, bananas grapesbananas Add to foods to give a sour taste Used as an antioxidantantioxidant levotartaric acid (D-()- tartaric acid) dextrotartaric acid (L-(+)- tartaric acid) mesotartaric acid
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  • Structural representation of sugars Fisher projection: straight chain representation Haworth projection: simple ring in perspective Conformational representation: chair and boat configurations
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  • Rules for drawing Haworth projections draw either a six or 5-membered ring including oxygen as one atom most aldohexoses are six-membered Aldotetroses, Aldopentoses, ketohexoses are five- membered Pyran Furan
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  • Rules for drawing Haworth projections Next number the ring clockwise starting next to the oxygen If the substituent is to the right in the Fisher projection, it will be drawn down in the Haworth projection (Down-Right Rule)
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  • Rules for drawing Haworth projections For D-sugars the highest numbered carbon (furthest from the carbonyl) is drawn up. For L-sugars, it is drawn down For D-sugars, the OH group at the anomeric position is drawn down for and up for . For L-sugars is up and is down
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  • Formation of the two cyclic forms of D-glucose Conformations: interconvertible without the breakage of covalent bonds, configurations : interconvertible only by breaking a covalent bondfor example, in the case of and configurations, Anomers: Isomeric forms of monosaccharides that differ only in the configuration about the hemiacetal or hemiketal carbon atom are called Mutarotation: interconvert of The and anomes of D- glucose in aqueous solution one-thirdtwo-thirds