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Lecture Ten : Carbohydrates

Biological Chemistry. First Year Organic Chemistry. Lecture Ten : Carbohydrates. Convener : Dr. Fawaz Aldabbagh. Carbohydrates C x (H 2 O) y – hydrates of carbon. Alternative name is saccharides. Glyceraldehyde is the simplest Monosaccharide. All Sugars from Natural Sources are D-Sugars.

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Lecture Ten : Carbohydrates

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  1. Biological Chemistry First Year Organic Chemistry Lecture Ten : Carbohydrates Convener : Dr. Fawaz Aldabbagh

  2. Carbohydrates Cx(H2O)y – hydrates of carbon Alternative name is saccharides Glyceraldehyde is the simplest Monosaccharide

  3. All Sugars from Natural Sources are D-Sugars No Correlation between D- and L- and optical rotation 2n stereoisomers Absolute configuration can only be determined by X-ray crystallography That is, the stereocenter most remote from the aldehyde group is on the right

  4. Professor Emil Fischer Nobel Prize 1902 One of the Fathers of modern chemistry Fischer was lucky with his assignment 16 stereoisomers

  5. ketohexose sugar Aldohexose sugar

  6. Hemi-acetal formation creates a new stereocentre at position 1 Anomeric carbon

  7. Five and Six –membered rings are easily formed and are often more stable than the open forms Five membered ring sugars are called Furanoses Six membered ring sugars are called Pyranoses Professor W. N. Haworth Nobel Prize 1937

  8. All equitorial –OH conformation is the most stable – b-anomer

  9. Like acetals, glycosides are stable in basic solutions but are hydrolysed by acids

  10. DISACCHARIDES Maltose is a Reducing Sugar Positive Test for Fehlings, Benedicts, Tollen’s One mole Acid-Hydrolysed or bya-glycosidase enzyme to 2 moles of D-glucose a -Glycosidic Linkage Sucrose is Table sugar & is a Non-Reducing Sugar One mole Acid-Hydrolysed or by sucrase enzyme to 1 mole of D-glucose and D-fructose Negative Test for Fehlings, Benedicts, Tollen’s

  11. Lactose is present in milk Lactose is a reducing sugar 1,4-b-glycosidic linkage between D-glucose and D-galactose POLYSACCHARIDES Polymers made of many sugar units held by glycosidic linkages Hydrolysed to maltose then D-glucose Glucans are the most common consisting of only glucose units Glucans include starch (principle food reserve of plants), Glycogen (principle food reserve for animals), and Cellulose principle structural material of plants

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