Chapter 7 Chem 341 Suroviec Fall 2016

Carbohydrates One of the 4 major classes of biomolecules Make up most of the organic matter on Earth Act as energy stores, fuels and metabolic intermediates Ribose and deoxyribose sugars form framework of RNA and DNA Polysaccharides make structural elements in cell walls Carbohydrates are linked to many proteins and lipids I. Monosaccarides (CH2O)n where n = 3-9 A. Naming Are aldehyde or ketone derivatives of straight chain polyhydroxy alcohols containing at least 3 C-atoms Carbonyl group = aldehyde = aldose Carbonyl group = ketone = ketose Ex: 3C = trioses 5C = pentoses

Aldoses

Ketoses

B. Determination of D or L 4 isomer positions 16 stereo positions 8 will be D 8 will be L D or L assigned by absolute configuration farthest from carbonyl group D-glucose

Configurations Predominate form of aldoses/ketoses are not in straight chain Monosaccharides with 5+ carbons usually cyclize 6-membered rings = pyranose 5-membered rings = furanose 2 anomeric forms of cyclic sugars  and  forms Carbonyl carbon = anomeric carbon = chiral center  form: OH group of the anomeric C is on OPPOSITE side of ring from CH2OH  form: OH group of the anomeric C is on SAME side of ring from CH2OH

C. Configurations Hexose and pentose can form pyranose or furanose forms Glucose usually pyranose Fructose 67% pyranose Ribose 75% pyranose Chair and boat conformations

D. Sugar derivatives Chemistry of monosaccharides is largely that of hydroxy and carbonyl groups Addition of amine - good for support in cell walls Deoxygenating - used in DNA Phosphoralation - used in energy storage 1. Redox Can be oxidized under mild conditions (Ag+, Cu2+) Can test for sugars: Fehlings (Cu2+) or Tollins (Ag+) test Only works for aldose sugars

2. Phosphorylation Important for metabolism First step in glucose breakdown to obtain energy Convert to glucose-6-phosphate Makes sugar anionic 3. Removal of -OH Where OH unit is replaced by H Called deoxy sugars -D-2-deoxyribose Component of DNA L-fucose One of few naturally occurring L sugars

Sucrose, maltose, lactose Linkage of 2+ sugars by glycosidic bond 4. Polysaccharides Sucrose, maltose, lactose Linkage of 2+ sugars by glycosidic bond Bond connecting anomeric C to the hydroxyl Sugars that have anomeric C that have not formed glycosidic bonds = reducing sugars Can go on to react further Are in equilibrium ring and linear forms

II. More Complex Polysaccharides Cellulose Serves structural role One of most abundant organic cmpds in biosphere Linear polymer chain (15,000 D-glucose (14)) Water insoluble (but glucose is?!?)

B. Carbohydrates Linked to Proteins Carbohydrate group can be covalently attached to a protein to form a glycoprotein Component of cell membranes, important for cell adhesion Human ABO blood has carbohydrates attached to proteins/lipids on surface of red blood cells All have common foundation (O) antigen A and B antigen have extra monosaccharide through -1,3 linkage Use of proper ABO blood group in transfusion critical, otherwise body rejects incompatible blood cells