L33-35 - Berg Tymoczko Stryer Biochemistry Sixth Edition...

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1 1 Biochemistry Sixth Edition Chapter 11: Carbohydrates Berg • Tymoczko • Stryer 2 Four major classes of biomolecules : 1.) Proteins 2.) Nucleic Acids 3.) Carbohydrates 4.) Lipids Chpt 11 Chpt 12 Chpts 4, 5 Chpts 2, 3 3 1.) Serve as energy stores, fuels, and metabolic intermediates. 2.) Ribose and deoxyribose sugars are the framework of RNA and DNA. 3.) Polysaccharides are structural elements of cell walls of bacteria and plants. •Cellulose is the most common organic compounds in the biosphere. 4.) Carboyhydrates are linked to many proteins and lipids. •Play key roles in intercellular communication. •Understanding the structure and effects of carbohydrate attachments on protein function is the field of ‘glycomics’. Carbohydrates are ubiquitous on Earth:
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2 4 Carbohydrates in food are an important source of energy •Starch, found in plant-derived food, consists of chains of linked glucose molecules. •Digested to individual glucose molecules •Generation of ATP •Building blocks of other molecules 5 11.) Carbohydrates are built up from monosaccharides: Aldehydes or ketones with multiple hydroxyl groups Monosaccharides: •small molecules •3-9 carbon atoms •vary in size and stereochemistry •can be linked together to form large oligosaccharides •can from a limitless number of structures--information-rich •[C(H 2 O)] n --literally, ‘hydrates of carbon’ C’s: 1 2 3 (=trioses) * * enantiomers keto group aldehyde group 6 Fischer projections of trioses 1 2 3 4 •D-configuration •See p27 for assigning stereochemistry. mirror plane
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3 7 D-aldoses •aldehyde •absolute configuration of D-glyceraldehyde at asymmetric center •tetrose (4C) •pentose (5C) •hexose (6C) •heptose (7C) •diastereomers •not enantiomers RNA epimeric at C-2 epimeric at C-4 •epimers are diastereomers that differ in configuration at a single asymmetric center •C(H 2 O) •asymmetry 8 D-ketoses •ketone •Note that ‘ C=O ’ is at C2 for ketoses, and C1 for aldoses. 9 Pentoses and hexoses cyclize to form pyranose and furanose rings •Aldohexoses cyclize to form pyranoses, 6-membered rings: * * α , β anomers (epimers that differ only at hemiacetal or hemiketal carbons; aka anomeric carbon,*) like Hawthorn projections <1% 33% 66% •to (R”O) is acetal
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This note was uploaded on 07/23/2008 for the course CHEM 476 taught by Professor Bevilacqua,philip during the Fall '07 term at Pennsylvania State University, University Park.

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L33-35 - Berg Tymoczko Stryer Biochemistry Sixth Edition...

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