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Condensation of two a -amino acids to form a dipeptide.

Condensation of two a -amino acids to form a dipeptide. N-Serine-Glycine-Tyrosine-Alanine-Leucine-C N-Ser-Gly-Tyr-Ala-Leu-C N-SGYAL-C. Sugars and Polysaccharides. Carbohydrates: carbon hydrates (CH 2 O) n or C n O n H 2n

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Condensation of two a -amino acids to form a dipeptide.

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  1. Condensation of two a-amino acids to form a dipeptide.

  2. N-Serine-Glycine-Tyrosine-Alanine-Leucine-C N-Ser-Gly-Tyr-Ala-Leu-C N-SGYAL-C

  3. Sugars and Polysaccharides Carbohydrates: carbon hydrates (CH2O)n or CnOnH2n Monosaccharides : n≥3, polyhydroxy aldehydes and polyhydroxy ketones (single unit). Essential components of all living organisms. -Aldose: aldehydic carbonyl or potential aldehydic carbonyl group -Ketose: ketonic carbonyl or potential ketonic carbonyl group Saccharides are also important components of nucleic acids, glycoproteins proteins and complex lipids.

  4. 1 2 3 Glyceraldehyde contains one chiral center* at C-2. In general n carbon aldoses contain 2n-2 stereoisomers. 1 2 3 Dihydroxyacetone the simplest ketose, does not contain an chiral center 1 2 3 4 Erythrulose, the second sugar in the ketose series, contains one chiral center at C-3. In general n carbon ketoses contain 2n-3 stereoisomers

  5. Nomenclature : - Fischer convention : D sugars have the same absolute configuration at the stereogenic center farthest removed from their carbonyl group as does D-glyceraldehyde. - The L version of the sugars are the mirror image of their D counterparts

  6. D-Xylose D-Arabinose

  7. D-Erythrulose

  8. L sugars are biologicaly much less abundant than D sugars. Know the structures of the sugars whose names are boxed. • Aldoses to remember are: D-glyceraldehyde, D-erythrose, D-ribose, D-mannose, D-galactose, D-glucose • Ketoses to remember are: Dihydroxyacetone, D-ribulose, D-xylulose, D-fructose

  9. Epimers

  10. Configurations and conformations Sugars can exist in several cyclic conformations, this is a consequence of the intrinsic chemical reactivity of the functional groups in the corresponding sugar Intramolecular reactions The reactions of alcohols with (a) aldehydes to form hemiacetals and (b) ketones to form hemiketals.

  11. The ring closure process renders the former carbonyl group asymetric: • !!!! New chiral center !!!! • The newly generated pair of diastereomers are call anomers and the • hemiacetal/ketal carbon is call anomeric carbon b anomer : OH substituent at the anomeric carbon is in the same side of the sugar ring from the CH2OH group at the chiral center that designates the D or L configuration a anomer : OH substituent at the anomeric carbon is in the opposite side of the sugar ring from the CH2OH group at the chiral center that designates the D or L configuration

  12. After dissolution in water: D-Glucose: Exclusively pyranose D-fructose: 67% pyranose, 33% furanose D-ribose: 75% pyranose, 25% furanose However, in polymers: Glucose: pyranose Fructose: furanose Ribose: furanose All the interconversions between furanose and pyranose form proceed through the linear form of the molecule. D-glucose is 33%  and 66% 

  13. Sugars are conformationally variable

  14. 2 forms of  glucose

  15. D-glucose is 33%  and 66%   glucose  glucose

  16. Monosaccharides are modified

  17. Monosaccharides are modified

  18. Oxidation reduction reactions : The aldehyde moiety in aldoses can be oxidize to yield a carboxylic acid, the resulting compounds are known as aldonic acids. Aldose Aldonic Acid Uronic Acid Glucose Gluconic Acid Glucuronic Acid

  19. Monosaccharides are modified

  20. - The reduction of the carbonyl group in aldoses and ketoses yields polyols known as alditols Ribitol Ribose

  21. Inositol Glycerol

  22. Gulonic Acid Glucose Gulose Gluconic Acid Ascorbic acid Gulono--lactone

  23. + 2e- Ascorbic acid Dehydroscorbic acid

  24. Sugar derivatives: The chemistry of sugars is largely that of their hydroxy and carbonyl groups. Glycosidic bonds: are analogous to the peptide bond in proteins, polysaccharides; are held together by glycosidic bonds between neigboring monosaccharides units

  25. a-glucose 6 5 6 4 1 5 2 3 4 1 2 3 b-glucose -glucose-(1,4)--glucose glucose-(14)-glucose

  26. -glucose-(1,4)--glucose glucose-(14)-glucose

  27. -glucose-(1,4)--glucose glucose-(14)-glucose

  28. -glucose-(1,6)--glucose glucose-(1)-glucose

  29. Trehalose -glucose-(1,1)--glucose glucose-(1)-glucose

  30. -galactose-(1,4)--glucose Galactose-(1)-glucose

  31. glucose-(1,4)--fructose glucose-(1)-fructose

  32. Polysaccharides

  33. Polysaccharides Cellulose Rigid - used for osmotic protection Load bearing function

  34. Degrading cellulose 1015 kg of cellulose synthesized and degraded annually Disaccharide product of breakdown is cellobiose Only microbes can do this!

  35. Chitin 1014 kg of chitin synthesized and degraded annually Exoskeltons for invertebrates -(1,4)-N-acetylglucosamine

  36. Storage Polysaccharides Starches Amylose Amylopectin Glycogen

  37. (1 - 4) Amylopectin Branched every 24 to 30 sugars

  38. Amylopectin Amylose

  39. Structure of glycogen. More extensively branched (every 8-12 sugars) Disaccharide breakdown products of starch are maltose and isomaltose

  40. Cell Walls and Connective Tissue

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