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Download Chapter 11. Carbohydrates
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Chapter 11. Carbohydrates • • • • Monosaccharides Oligosaccharides Polysaccharides Glycoproteins Carbohydrates • Gluconeogenesis and photosynthesis • Oxidation of carbohydrates provides energy to sustain life • Energy storage — starch or glycogen • Structural function – cellulose, chitin peptidoglycan & glycosaminoglycans • Glycoconjugates - glycoproteins & glycolipids Classification of monosaccharides • Chemical nature of carbonyl group – Aldose : carbonyl is an aldehyde – Ketose : carbonyl is a ketone • Number of carbon atoms – – – – – – Trioses (C3) Tetroses (C4) Pentoses (C5) Hexoses (C6) Heptoses (C7) etc D-Aldoses D-Ketoses ketotriose ketotetrose ketopentoses ketohexoses Epimers Sugars that differ only by the configuration around one carbon atom Hemiacetals and hemiketals Cyclization of monosaccharides Cyclic sugars have two anomeric forms α-anomer β-anomer Sugars are conformationally variable Two chair conformations of β-D-glucopyranose Sugar derivatives • Aldonic acids – oxidation of an aldehyde group in an aldose to an carboxylic acid • Uronic acids – oxidation of a primary alcohol group to an carboxylic acid • Alditols – reduction of aldoses and ketoses • Deoxy sugars – replacement of OH with H • Amino sugars – replacement of OH with NH2 • Sugar phosphates Aldonic acids and uronic acids D-Glucose D-Gluconic acid D-Glucuronic acid Alditols Deoxy sugars Amino sugars (NAM) Sialic acids Sugar phosphates O-Glycosides N-Glycosides French Fries à la Plastic Neurotoxin and suspected carcinogen !!! Disaccharides Artificial sweeteners Saccharin Aspartame Sucralose Polysaccharides (Glycans) Polymers of monosaccharides linked together by glycosidic bonds • Homo or heteropolysaccharides • Linear or branched polysaccharides Storage polysaccharides • Starch – Plant • Glycogen – Animal Starch granule in plant cell chloroplasts Glycogen granule in liver cells Starch Helical structure of amylose Glycogen Structure of amylopectin or glycogen Structural polysaccharides • Cellulose – Plant cell walls – Marine invertebrates (Tunicates) • Chitin – Exoskeletons of invertebrates (Crustaceans, Insects, Spiders) – Cell walls of most fungi and many algae • Glycosaminoglycan (=Mucopolysaccharides) – Connective tissues (Cartilage and tendons) or extracellular matrix (ground substance) of higher animals Cellulose n Glucose Glucose Chitin Glycosaminoglycans (Mucopolysaccharides) n n n n n n Glycosaminoglycans • Hyaluronic acid – connective tissue, synovial fluids, vitreous humor of the eye • Chondroitin sulfate – cartilage and other connective tissue • Dermatan sulfate – skin • Keratan sulfate • Heparin – component of intracellular granules of the mast cells (blood-clotting inhibitor) • Heparan sulfate – cell surface and extracellular substance in blood vessel and brain (interaction with fibroblast growth factors and their receptors) Glycoproteins • Proteoglycans • Peptidoglycans • Glycosylated proteins Proteoglycans Bacterial cell walls Peptidoglycans Antibiotics targeting peptidoglycans Glycosylated proteins • Proteins often contain oligo or polysaccharides • Sugar modification are mostly seen in extracellular or transmembrane proteins • Protein can contain 10-90% carbohydrates • Carbohydrates are usually linked through asparagine (N-linked), or serine or threonine (O-linked) O- and N-linked oligosaccharides Oligosaccharide dynamics Turnover of serum proteins Cell surface Lectins Proteins that specifically recognize carbohydrate ABO blood types
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