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Carbohydrates and Glycobiology

Carbohydrates and Glycobiology. Carbohydrate function and classification Monosaccharides Chemical structure and properties Linear and cyclized forms Common monosaccharides and disaccharides Carbohydrates can be joined to phosphates , alcohols and amines

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Carbohydrates and Glycobiology

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  1. Carbohydrates and Glycobiology • Carbohydrate function and classification • Monosaccharides • Chemical structure and properties • Linear and cyclized forms • Common monosaccharides and disaccharides • Carbohydrates can be joined tophosphates, alcohols and amines • Hexose derivatives important in biology • Polysacchardies: Glycogen, Starch, Cellulose, and Chitin

  2. “The chemistry and biology of carbohydrates has been a Cinderella field: an area that involves much work but, alas, does not get to show off at the ball with her cousins, the genomes and proteins.” Stella Hurtley, Robert Service, Phil Szuromi, Science Vol 291, 23 March 2001

  3. “What has rescued this Cinderella from the shadows is no fairy godmother but a plethora of new synthetic and analytic methods that a previous generations of researchers would have found nearly magical nonetheless.” “Glycobiology has finally become part of the mainstream”

  4. Carbohydrates • Functions: • As energy stores and fuels • As metabolic intermediates • As part of many important molecules (ATP, ribose sugar..) • In polysaccharides(e.g. cell walls of bacterial and plant) • Linked to proteins and lipids (glycoconjugates) • In the extra cellular milieu, they exert effects on cellular recognition in infection, cancer, and immune response. • Carbohydrates are central to many processes that are at the core of important diseases  drug design targeting a wide spectrum of diseases • Classification: mono- and polysaccharides

  5. Monosaccharides • Two families of monosaccharides • Aldehydes with multiple OH groups (aldose) • Ketones with multiple OH groups (ketose) • Chemical structures of monosaccharides • Triose, tetrose, pentose, hexose, heptose • Smallest one: (CH2O)3 e.g.: D(L)-glyceraldehyde • Hexoses are the most common monosaccharides in nature • D-ribose and 2-deoxy-D-ribose are components of nucleotides and nucleic acids • All except one monosaccharides have asymmetric centers • Fisher projection representation • Perspective representation

  6. Cyclized forms are predominant for pentoses and hexoses • Furanose (hemiacetal): cyclized pentose • Pyranose (hemiketal): cyclized hexose • Haworth projections • Anomers • Conformation of pyranose/furanose rings • Pyranose ring: Chair vs. boat form • Furanose ring: puckered

  7. Common Monosaccharides and Disaccharides • Common monosaccharides • D-ribose, D-glucose, D-mannose, D-galactose, D-fructose • Common disaccharides and enzymes that hydrolyze them • Sucrose: glucose-fructose (sucrase) • Lactose: galactose-glucose (lactase) • Maltose: glucose-glucose (maltase) • Enzymes are located on epithelial cells lining the small intestine • Many monosaccharides are reducing agents • Lactose intolerance: lack oflactase

  8. Carbohydrates Can be Joined to Phosphates, Alcohols and Amines • Sugars can be phosphorylated • Key intermediates in energy generation and biosynthesis • Carbohydrates can be joined to alcohols and amines by glycosidic bonds • N-glycosidic • O-glycosidic • Important hexose derivatives in biology (next slide)

  9. Some hexose derivatives important in biology a uronic acid a aldonic acid

  10. Polysaccharides: Glycogen • Polysaccharides • Homosaccharides (branched and unbranched) • Heterosaccharides (branched and unbranched) • Glycogen • Store of glucose in animal cells • 14 linkage with 16 branch • Exist in granules inside the cell tightly bound with enzymes for glycogen synthesis and degradation

  11. Polysaccharides: Starch • Starch • Store of sugar in plants • Two forms • Amylose: unbranched • Glucose, -1,4 linkage • Amylopectin: branched • Glucose, 1 -1,6 per 30 -1,4 • -amylase: hydrolyze -1,4 linkages

  12. Curved Polysaccharide Chain in amylose-Unbranched Starch

  13. Polysaccharides: Cellulose and Chitin • Cellulose • Plant polysaccharide • Serve as a structural not nutritional role • Unbranched polymer of glucose, -1,4 linkages • Linear chains; forming fibers; high tensile strength • Mammals lack cellulases and so cannot digest wood and vegetable fibers • Chitin • Exoskeletons of insects • Unbranched polymer of NAG, -1,4 linkages • Long straight chains; structural roles

  14. Linear Structure of Cellulose (D-glucose b1 4 Linkage) Extended chain Give extended chain Intra-chain H-bonds Inter-chain H-bonds

  15. Bacterial Cell Walls Contain Peptidoglycans NAG: N-acetylglucosamine NAM: N-acetylmuramic acid b 1 4 linkage A number of layers; Provide strength to the cell; Keep shape of the cell; Antibacterial agent act on cell wall –peptidoglycan; Pennicillin; Lysozyme Structure of the cell wall of staphylococcus aureus

  16. Glycosaminoglycansare components of the extracellular matrix the extracellular space in the tissues of multicellular animals a gel-like material Heteropolysaccharide; linear Repreating disaccharides; C-6 carbon in glucose/galactose/ mannose is oxidized to carboxyl Uronic acid (in most cases): D-glucuronic acid, or L-iduronic acid N-acetylglucosamine (NAG) or N-acetylgalactosamine; One or more –OH is esterified with sulfate High density of negative charges on glycosaminoglycans (-COO-, -OSO3-) extended conformation

  17. Uronic acid (most cases) NAG or N-acetylgalactosamine Hyaluronate Very long! In some glycosaminoglycans, The amino sugar is esterified with sulfate Chondroitin 4-sulfate short High density of negative charges extended conformation in solution Keratin sulfate short Glycosaminoglycans are attached To extracellular proteins to form proteoglycans

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