CHAPTER 7 (Picture)

CHAPTER 7 (Picture) - David L. Nelson and Michael M. Cox...

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1 Lehninger Principles of Biochemistry Fourth Edition Chapter 7: Carbohydrates and Glycobiology David L. Nelson and Michael M. Cox
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2 Introduction Carbohydrates are the most abundant biomolecules on earth. Function of carbohydrates include: 1. Energy source via oxidation of sugars and starch. 2. Structural and protective elements – insoluble carbohydrate polymers – found in: Cell walls of bacteria and plants Connective tissues of mammals. 3. Lubricants – skeletal muscles 4. Recognition molecules and adhesion between cells 5. Glycoconjugates –carbohydrates covalently linked to
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3 Introduction Definitions Monosaccharides (simple sugar) – consists of a single polyhydroxy aldehyde or ketone unit. Most abundant is Glucose . Oligosaccharides – consists of short chains of monosaccharide units or residues joined together by glycosidic bond . Disaccharides – consists of two monomer units. Polysaccharides – contain more than 20 monomer units.
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4 Two families of monosaccharides are Aldose and Ketose (Fig. 7-1) . Aldose – carbonyl group at the end is an aldehyde. Ketose - carbonyl group at the end is a ketone
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5 Introduction Monosaccharides except for dihydroxyacetone contain one or more chiral carbon atoms – optically active ( Fig.7-2 ). In general, a molecule with n chiral centers have 2 n stereoisomers. D-stereoisomers of aldose and ketose with 3 – 6 carbon atoms are shown in Fig. 7-3 .
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10 Epimers – two sugars that differ only on the configuration around one carbon ( Fig. 7-4 )
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11 Cyclic structure of monosaccharides In aqueous solution, aldotetroses and all monosaccharides with 5 or more carbon atoms in the backbone exits as cyclic (ring) structure. Examples (Fig. 7-6) D- glucose exist in solution as cyclic structures in which free hydroxyl group at C-5 has reacted with the aldehydic C-1 to give α and β stereoisomers. The six-membered ring compound is called pyranose because it resembles pyran ( Fig 7-7). Aldohexoses also exit in a 5-membered rings called furanoses – resemble furan.
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15 Oxidation of Monosaccharides -Monosaccharides can be oxidized by mild oxidizing agents as ferric or cupric ions ( Fig. 7-10a ). -The carbonyl carbon group is oxidized to carboxyl group. -Reducing sugars include glucose
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16 Introduction Use of this property Fehling’s reaction – qualitative test for reducing sugars. Medical application : Previously was used to detect and measure elevated glucose levels in blood and urine in the diagnosis of diabetes mellitus . More sensitive method of glucose oxidase ( Fig. 7- 10b ) has replaced Fehling test in diabetes diagnosis.
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17 Introduction Diasaccharides Examples are maltose, lactose and sucrose. Consists of two monosaccharides joined covalently by an
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This note was uploaded on 08/21/2008 for the course BIOCHEM 301 taught by Professor Vanes during the Spring '08 term at Rutgers.

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CHAPTER 7 (Picture) - David L. Nelson and Michael M. Cox...

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