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Cha 5 - Carbs.docx

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McMaster University
Lovaye Kajiura

Chapter 5 – Carbohydrates - Monomers  monosaccharides - Small polymers  oligosaccharides - Large polymers  polysaccharides - Carbs : carbonyl and hydroxyl functional groups; C-H bonds Section 5.1 – Sugars As Monomers - Chemical energy - Building blocks for more complex compounds - Sugar (ribose)  important for formation of nucleotides Monosaccharide – simple sugar; (CH 2) nnd cannot be hydrolyzed to form smaller carbohydrates - Carbonyl group (either terminal or within chain) - Terminal  form aldehyde sugar (aldose) - Within carbon chain  form ketone sugar (ketose) - Presence of carbonyl group and multiple hydroxyl group  array of functional groups in sugars Trioses – three-carbon sugars Pentose – five carbons (ex. ribose) Hexose – six-carbon sugar - Variation for location of carbonyl group and total # of carbons - Vary in spatial arrangement o Differ in configuration of hydroxyl functional groups - Chain/ring form – exist in equilibrium when simple sugars are in solution - Tend to be ring structures o Ex. glucose – rarely exists in linear form o -Glucose  hydroxyl group (on carbon 1) below plane of ring o -Glucose  hydroxyl group above plane of ring - Several monosaccharides due to variation in structure o Alternative ring forms o Optical isomers w/ diff. arraignments of hydroxyl groups in space o Diff. mirror-image forms o Variation in carbon # o Aldose/ketose placement of carbonyl group Chemical evolution - Monosachharides readily synthesized under mimicked conditions of prebiotic soup - Questions concerning why ribose dominated and how monosaccharides formed complex polysaccharides found in today’s cells Section 5.2 – Structure of Polysaccharides - Poly – form from monosaccharides (linked together) - Disaccharides – simples poly; two sugars - Simple sugars polymerize (condensation reaction b/w two hydroxyl groups)  result in glycosidic linkage (covalent bond) - Glycosidic linkages  occur b/w hydroxyl groups o Location/geometry of glycosidic linkages can vary widely among polysaccharides (due to variation of hydroxyl group locations in monosaccharides) Storage Polysaccharide in Plants - Starch – monosaccharides stored in form of starch for later use (in plants) - Consists of -glucose monomers joined by glycosidic linkages - Unbranched helix (amylose) o Only -1, 4-glycosidic linkages - Branched helices (amylopectin) o Forms because of linkage b/w carbon 1 of glucose monomer and carbon 6 of another glucose monomer o -1,6 glycosidic linkages 1 out of every 30 monomer Glycogen: Highly Branched Storage Polysaccharide in Animals - Glycogen – storage role in animals o Liver and muscles - Broken down into glucose monomers - Used for energy - Polymer of -glucose o -1,6 glycosidic linkages 1 out of every 10 glucose subunits - Highly branched helices Cellulose: Structural Polysaccharide in Plants - Cell wall – protective sheet that occurs outside membrane - Composed primarily of one or more polysaccharides - Cellulose – main component in cell wall - Polymer  -glucose monomers o -1,4 linkages o Glucose monomer – flipped in relation to adjacent monomer o Increase stability of cellulose strands  allows multiple H-bonds to form b/w adjacent/parallel strands of cellulose - Parallel strands joined by H-bonds o Linked cellulose fibers  strong and provide structural support Chitin: Structural Polysaccharide in Fungi and Animals - Polysaccharide - Stiffens cell
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