369Lecture12_F11(1) - 1 CH369 Fall 2011 Lecture 11 Ch 11...

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+ Lecture 11: Ch 11 Carbohydrates CH369 Fall 2011 1
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+ Reactions of Aldehydes & Ketones 1 acetal group 1 ketal group 2 acetal groups 2 ketal groups 2
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+ Fischer projection Haworth projections Anomeric C is an alcohol Cyclization of Sugars Monosaccharide can bite its own tail C1 is anomeric carbon C1 condenses w/ O5 to form intramolecular hemiacetal Right on Fischer = Down on Haworth α = down (right on Fischer) β = up (left on Fischer) Equilibrium between closed and open forms makes anomeric C reactive 3
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+ Mutarotation: Interconversion of α - and β - anomers Fischer projection Chain form Glucose anomers (aqueous solution) 36% 64% 4
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+ Reducing Sugars Reducing sugars are carbohydrates that can reduce oxidizing agents Carry reactive carbonyl group Sugars which form open chain structures with free carbonyl group Reduction of metal ions Benedict’s reagent: CuSO 4 in alkaline solution 5
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+ Sugar Derivitization Reaction of glucose with methanol yields addition of methoxy group to anomeric carbon No longer reactive Now a non-reducing sugar Group linked to anomeric C forms glycosidic bond Glycoside is sugar linked to another molecule 6
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+ Sugar Derivitization Sugars can also be phosphorylated Gly-3-P F-6-P Important intermediates in metabolic pathways Hydroxyl group can be replaced with amino group Glucosamine Oxidation of sugar gives uronic acids Reduction gives sugar alcohol Ribose converted to deoxyribose 7
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+ Polysaccharides 8 Chains or polymers of carbohydrates Formed by glycosidic bonds Aka glycan chains Can be used to modify other molecules, e.g. glycoproteins or glycolipids Polysaccharides a common fuel-storage molecules Can be joined in a variety of ways Tremendous repertoire of complex molecules! Multiple –OH groups with different bonding arrangements makes this possible Need way to classify and understand them that includes this level of complexity Glycomics Study of carbs http://faculty.washington.edu/dratner/Research.html
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+ Which of these is a nonreducing sugar? 9 A.(a) B.(b)
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+ Common Disaccharides Disaccharides occur in nature most commonly as breakdown products of polysaccharides Lactose Secreted in milk of lactating mammals Galactose- -1,4-glucose Galactose and glucose, joined by glycosidic bond between #1 C of galactose and the #4 C of glucose If different C’s were joined to form the bond – we’d have a different disaccharide Most adult mammals (including humans) produce very little lactase ( -galactosidase) and have some difficulty in digesting this sugar 10
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+ Structural Carbohydrates Cellulose Glucose polymer formed between #1 and #4 C atoms – like amylose Linkages are Makes for very profound differences in structure Instead of compact granules (storage form), form extended fibers Provides rigidity and strength for plant cell walls Extensive H-bonding network within and between adjacent chains 11 Animals don’t make it and most cannot digest it Microbes do Normal microflora for ruminants Celluose fibers
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