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Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,*,Qin, Yongmei,PhD,(,秦咏梅,),Chapters included:,May 26,Chapter 7,Carbohydrates & Glycobiology,June 2,Chapter 10 Lipids,June 9,Chapter 11 Biological Membranes and Transport,June 16,Chapter 12 Biosignaling,Contact information:,email: qinym,Tel: 6275 8885,Address: New building of our college: Room 214,Chapter 7,Carbohydrates & Glycobiology,Lectured by Dr. Qin Yongmei (,秦咏梅,): May 26, 2007,Reference:,Carbohydrates: the Sweet Molecules of Life,by Robert V Stick,What do we eat,high protein, low-carbohydrates, no-fat,Science is evolutionary, and new research points in different directions are coming up every day.,But, there isnt enough research on nutrition and popular diets to prove anyone right or wrong.,Carbohydrates in food are important sources of energy,Upland cotton produces the most widely used,natural fibers,cellulose (a polysaccharide),Cellulose:,the most abundant organic,compounds in the biosphere,10,15,kg of cellulose is,synthesized and degraded,on Earth each year,Carbohydrates & Glycobiology,Carbohydrate, (C-H2O)n = “Carbon + Water,Source of energy,Structure (cotton fibers: cellulose),Building blocks,Cellular recognition,Contents,Monosaccharides,and disaccharides,Polysaccharides,Glycoconjugates,:,proteoglycans,glycoproteins,glycolipids,Working with carbohydrates,Monosaccharides and disaccharides,Monosaccharides,contain either:,aldehyde,group (,aldoses,),ketone,group (ketoses),Two common hexoses:,Pentoses: components of nucleic acids,(present in RNA),(present in DNA),2. Monosaccharides can be classified,according to the number of carbons:,triose,3 carbons,tetrose,4 carbons,pentose5 carbons,hexose,6 carbons,heptose,7 carbons,4. Monosaccharide stereoisomers,How many stereoisomers does an aldohexose contain,3. Naming stereoisomers,3 ways to represent the,two steroisomers of glyceraldehyde,enantiomer,D-Aldoses,(triose),(tetrose),(pentose),(hexose),D-ketoses,Ketoses have one fewer asymmetric center than do aldoses with the same number of carbons,Note:,Epimers:,two sugars that differ only in the,configuration around one carbon atom,D-glucose and two of its epimers,5. Formation of hemiacetal or hemiketal can,occur within a monosaccharide,Two,monosaccharides,are,connected through,glycosidic,linkage,to form disaccharides.,O-glycosidic,bond,reducing,end,hemiacetal,acetal,aldehyde,Only,aldoses,having,five or more carbon,atoms can form,pyranose rings,mutarotation,Anomers:,differ in their,configuration,about either,hemiacetal or,hemiketal,carbon atom,Anomers,(two cyclic forms of D-glucose),Create an asymmetric,center,C-1: anomeric,carbon atom,Haworth perspective formulas :,commonly used to show the stereochemistry of ring forms of monosaccharides,Fructose can form both five-membered furanose and,six-membered pyranose rings,predominate in,many fructose,derivatives,predominate in,fructose free,in solution,Conformation of pyranose rings,The chair form is more stable because of less,steric,hindrance,as the axial positions are occupied by,hydrogen atoms.,b,-D-glucopyranose,steric,hindrance,(predominated form),6. Reactions of monosaccharides,The,aldehyde,and primary alcohol,groups can be oxidized to acids,(,aldonic,and,uronic,acids),reducing,sugar,oxidation,Application to diagnosis of diabetes mellitus,(determination of glucose concentration),Fehlings reaction,More sensitive method: using glucose oxidase,7. Monosaccharide derivatives,aldonic acid,uronic acid,8. Formation of disaccharides,Two,monosaccharides,are,connected through,glycosidic,linkage,to form disaccharides.,O-glycosidic,bond,reducing,end,Some common disaccharides,Nonreducing,sugar !,C,ontains no free,anomeric,carbon atom,nonreducing,disaccharides,are named as,glycosides,Some rules to name oligosaccharides,Give the configuration at the anomeric carbon joining the first,monosaccharide unit to the second.,Name the nonreducing reside; to distinguish five- and six-membered,ring structures, insert “furano or “pyrano into the name.,Indicate the parentheses the two carbon atoms joined by the,glycosidic bond, with an arrow connecting the two numbers.,Name the second reside. If there is a third residue, describe the,second glycosidic bond by the same conventions.,Example:,maltose,conventional name:,-D-glucopyranosyl-(14)-D-glucopyranose,simplified name:,Glc (, 14,) Glc,Polysaccharides,(glycans),As high as 2 x 10,7,Daltons,Storage forms of glucose,starch (plant),amylose,(un-branched),amylopection,(branched),glycogen (animals),Structural roles,Cellulose (,eg,. cotton),Chitin (Arthropods),Glycosaminoglycans,(animals),Differences between,homopolysaccharides,and,heteropolysaccharides,2. Homopolysaccharides,Starch (amylose, amylopectin),unbranched,polymer of D-glucose-,a,(1,4)-D-glucose,branched polymer of D-,glucose-,a,(1,4)-D-glucose with,a,(1,6) branch point,A cluster of amylose and amylopectin,(in starch granules),strands of,amylopectin,form,double-helical,structures,with each other or with,amylose,strands,Glucose residues at the nonreducing ends are removed enzymatically during mobilization,of starch for energy production.,3. Some homopolysaccharides serve structural roles,Cellulose,unbranched,polymer of D-glucose-,b,(1,4)-D-glucose,the,b,configuration,allows cellulose to form very long,and straight chain.,scale drawing of segments of two parallel cellulose,chain,3. Some homopolysaccharides serve structural roles,Chitin,unbranched,polymer of D-N-,acetylglucosamine-,b,(1,4)-D-N-,acetylglucosamine,4. Steric factors and hydrogen bonding influence,homopolysaccharide folding,The folding of polysaccharides in three dimensions follows the same principles as those governing polypeptide structure:,hydrogen boding,hydrophobic interactions,van,der,Waals,interactions,electrostatic interactions,The three-dimensional,structures are described,in terms of dihedral,angles, analogous to,angles made by the peptide,bond.,gal(,1,3)gal,Relative energy,A map of favored conformations for oligosaachrides,and polysaccharides,The structure of starch (amylose),Coiled helical,structure,Most stable conformation,is curved, rather than linear,From the structures of cellulose and starch (glycogen),we learn:,The different consequences of the,a,and,b,linkages,have biological significance.,The straight chain formed by,b,linkages is optimal for,the construction of fibers having a high tensile strength.,The open helix formed by,a,linkages is well suited to,form an accessible store of sugars.,Mammals lack,cellulases,that therefore cannot digest,wood and vegetable fibers.,Why not store glucose in its monomeric form,It has been calculated that,hepatocytes,store,glycogen equivalent to glucose = 0.4M; the actual,glycogen = 0.01,mM,.,If,in,cytosol,glucose = 0.4 M, leading to osmotic entry,of water that might rupture the cell.,If intracellular glucose = 0.4 M, compared with,extracellular,(in blood of a mammal) glucose = 5,mM,the free-energy change for glucose uptake into cells,would be prohibited.,4. Bacteria and algal cell walls contain structural,heteropolysaccharides,alternating (,b,1,4)-linked N-,acetylglucosamine,and N-,acetylmuramic,acid residues,Peptidoglycan of the cell wall,of,Staphlococcus aureus,5. Glycosaminoglycans are heteropolysaccharides,of the extracellular matrix,At least one of sugars in the repeating unit has,a negatively charged,carboxylate or,sulfate group,-D-Glucuronate,透明质酸,软骨素,硫酸角质素,肝素,透明质酸:存在于眼球玻璃体、关节液和皮肤等组织中作为润滑剂和撞击缓冲剂，并有助于阻滞入侵的微生物及毒性物质的扩散。,2. 硫酸软骨素:动物组织的根底物质，用以保持组织的水分和弹性。包括软骨素、等数种，软骨素是软骨的主成分。和肝素相似，可用以降血脂，改善动脉样硬化病症。此外，硫酸软骨素还有消除皱纹、使皮肤保持及富弹性的作用。硫酸软骨素主要存在于鸡皮、鱼翅、鲑鱼头和鸡等软骨内。,3. 肝素:高度硫酸酯化的右旋多糖，与蛋白质结合大量存在于肝脏之中，其他器官和血液中也有。肝素有强的抗凝血作用，临床上用肝素钠盐预防或治疗血栓的形成，肝素也有消除血液脂肪的作用。,proteins: fibroblast growth factor,(FGF1),FGFR (R: receptor),ligand: heparin,Their interaction: electrostatic interaction,Glycoconjugates:,proteoglycans,glycoproteins,& glycolipids,Proteoglycans:,macromolecules of the cell surface or,extracellular matrix in which one or more,glycosaminoglycan,chains are joined covalently to a membrane protein or a,secreted protein,Glycoproteins:,proteins covalently attached by one or several,oligosaccharides,Glycolipids,: membrane lipids in which the hydrophobic head groups are oligosaccharides.,1. Proteoglycans: glycosaminoglycan-containing,macromolecules,(glycosaminoglycan),(linker),Function as lubricants and structural components in,connective tissue, mediate adhesion of cells to the,extracellular matrix and bind factors that stimulate,cell proliferation,NA domain:,N-acetylated domain,S domain:,Sulfated domain,Proteoglycans structure of an integral membrane protein,Proteoglycans form aggregates,at the extracellular matrix,Proteoglycan aggregates,can interact with collagen,in the extracellular matrix,of cartilage, contributing,to the development and,tensile strength of the,connective tissue.,Proteoglycans resemble polysaccharides more than proteins,as much as the carbohydrate makes up as much as 95% of,the biomolecule by weight,the association between cells,and the proteoglycan of extra-,cellular matrix is mediated by,a membrane protein (,integrin,),and by an extracellular protein,(,fibronectin,) with binding sites,for both integrin and the,proteoglycan.,Cell matrix interactions,anchor cells to,extracellular,matrix,direct t,he,migration of cells in,developing tissue,convey information in both,directions across plasma,membrane (via,integrins,),2. Glycoproteins are information-rich containing,oligosaccharides,glycosidic bond,N-glycosyl bond,How are glycoproteins sorted in the cell,A,pentasaccharide core,is common to all N-linked,oligosaccharides and serves as the foundation for,a wide variety of N-linked oligosaccharides,What are the biological advantages of adding,oligosaccharides to proteins,alter the,polarity,and,solubility,of their,conjugated proteins,influence,protein-folding,events,protect some proteins from attack by,proteolytic,enzymes,complex of oligosaccharides is enormously,rich in,structural information,some proteins present,tissue,glycoforms,(may act as a tissue-specific mark),Calnexin,(chaperone),Calnexin,(chaperone),An unfolded or,misfolded,protein,will,receive a glucose residue,;,Such,glycosylated,protein bind to,calnexin,that allow multiple,attempts to attain correct folding;,Properly folded proteins are not re-,glucosylated,3. Glycolipids and lipopolysaccharides are,membrane components,Gangliosides:,membrane glycolipids,of eukaryotic cells in,which the polar head,group forms the outer,surface of the membrane,Example: the oligosaccharide moieties of,the gangliosides determine human,blood groups,Lipopolysaccharides:,dominant surface feature,of the outer membrane,of gram-negative bacteria.,- target of antibody,- toxic to humans,The principal determinant of the serotype,(immunological reactivity) of the bacterium,4. Oligosaccharide-lectin interactions mediate,many biological processes,Lectin:,proteins that bind carbohydrates with high affinity,(hydrogen-bonding),and specificity,(,lecitins,can be,easily distinguished by their binding with various,similar sugars).,involved in a wide variety of cell-cell recognition,and adhesion processes,Selectins:,a family of lectins, found in plasma membranes, that mediate cell-cell,recognition and adhesion.,Role of lectin-ligand interactions in,lymphocyte movement to the site,of an infection or injury,Helicobacter pylori,cells,adhering to the gastric surface,causes,ulcers,by interactions,between,a bacterial surface lectin,and the,Le,b,oligosaccharide,(a blood,group antigen) of the gastric,epithelium,Lectin-Carbohydrate Interaction-,very strong & highly specific,Neu5Ac,(N-acetylneuraminic,acid) binding site,mannose 6P,Ca,2+,Sialic acid-specific lectin,Mannose 6P receptor,Roles of oligosaccharides in recognition and adhesion,at the cell surface,Working with carbohydrates,Analyze composition of,monosaccharides,(high-performance liquid chromatography, HPLC or,gas-liquid chromatography ),Determination of,position(s,) of,glycosidic,bonds,Methylate,free hydroxyl group (-OH) by CH,3,I,then hydrolyze the,methylated,polysaccharide,in acid. The only free -,OH(s,) present in the,monosaccharide are those involved in,glycosidic,bonds,Determination of sequence of,monosaccharides,Mass spectrometry and NMR spectroscopy,MALDI-TOF spectrometry,Enzymatic hydrolysis with specific glycosidase,peptide N-glycosidase F,& neuraminidase,peptide N-glycosidase F,& neuraminidase &,b,-1,4-galactosidase,Summary,Sugars,are compounds containing an,aldehyde,or,ketone,group and two or more hydroxyl groups;,Monosaccharides,generally contain several,chiral,carbons,and therefore exist in a variety of,stereochemical,forms;,Monosaccharides,commonly form internal,hemiacetals,or,hemiketals,;,A,hydroxy,group of one monosaccharide can add to the,anomeric,carbon of a second monosaccharide to form an,acetal,. In this,disaccharide, the,glycosidic,bond protects,the,anomeric,carbon from oxidation;,Oligosaccharides,are short polymers of several,monosaccharides,joined by,glycosidic,bonds;,The common,nomenclature,for,di,- or oligosaccharides,specifies the order of monosaccharide units, the,configuration at each,anomeric,carbon, and the carbon,atoms involved in the,glycosidic,linkage (s);,Polysaccharides,(,glycans,) serve as stored fuel and as,structural components of cell walls and,extracellular,matrix;,The,homopolysaccharides,starch and glycogen are stored,fuels in plant, animal, and bacterial cells.,The,homopolysaccharide,cellulose, chitin, and,dextran,serve structural roles.,Homopolysaccharides,fold,in three dimensions;,Bacterial and algal cell walls are strengthened by,heteropolysaccharides,-,peptidoglycan,in bacteria, agar,in red algae;,Glycosaminoglycans,are,extracellular,heteropolysaccharides,in which one of the two monosaccharide units is,a,uronic,acids,and the other an,N-acetylated amino sugars,.,Proteoglycans,and,glycoconjugates,in which a core protein is,attached covalently to one or more large,glycans,.,Proteoglycans,provide points of adhesion, recognition, and,information transfer between cells, or between the cell,and the,extracellular,matrix.,Glycoproteins,contain covalently linked oligosaccharides,that are smaller but more structurally complex, and,therefore,more information-rich than,glycosaminoglycans,.,The covalently attached oligosaccharides influence the,folding and stability of the protein, provide critical,information about the targeting of newly synthesized,proteins, and allow for specific recognition by other,proteins.,Glycolipids,and,lipopolysaccharides,are components of the,plasma membrane with covalently attached oligosaccharide,chains exposed on the cells outer surface.,Lectins, proteins with highly specific carbohydrate-binding,domains, are commonly found on the outer surface of cells,where they initiate interaction with other cells. The,adhesion of bacterial and viral pathogens to their animal-,cell targets occurs through binding of,lectins,in the,pathogens to oligosaccharides in the target cell surface.,Selectins,are plasma membrane,lectins,that bind,carbohydrate chains in the,extracellular,matrix or on the,surface of other cells, thereby mediating the flow of,information between cell and matrix or between cells.,Establishing the complete structure of oligosaccharides,and polysaccharides,requires determination of branching,positions, the sequence in each branch, the configuration,of each monosaccharide unit, and the positions of the,glycosidic,links.,
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