生物化学教学课件：第一章 糖

1、Biochemistry1. Existence Carbohydrates are the most abundant biomolecules on earth. 2. Saccharides play a variety of roles in living organisms:Energy storage (monosaccharides and oligosaccharides and polysaccharides)Structural roles(polysaccharides)Cell identity (oligosaccharides)Carbohydrate / Sacc

2、harides3. Definition and classification of saccharideCarbohydrates are polyhydroxy aldehydes or ketones,or substances that yield such compounds on hydrolysis.Empirical formula (CH2O)n; some also contain nitrogen, phosphorus, or sulfur.Classification of saccharideThree major size classes of carbohydr

3、ates: MonosaccharidesSaccharide Oligosaccharides Polysaccharides: homopolysaccharide, heteropolysaccharide, glycoconjugate 4. Structure of monosaccharideStraight-chain structure of monosaccharidecarbonyl group：醛糖aldose, 酮糖ketosecarbon atoms in the backbone：3,4,5,6,7 trioses, tetroses, pentoses, hexo

4、ses, and heptoses不对称碳原子(asymmetric carbon atom)C*（chiral carbon）Fisher projection单糖构型configurationD，L nomenclatureThe enantiomers 对映异构体 of glyceraldehydeConfiguration of monosaccharide: based on 甘油醛 glyceraldehyde Compare the configuration of the chiral center most distant from the carbonyl carbon.O

5、ptically active isomers旋光异构Monosaccharide has optical activity单糖具有旋光性左旋(levorotatory), “-”右旋(dextrorotatory), “+”旋光率(specific rotation)D、L mean configuration构型+、- mean the optical activityThe predominant monosaccharides in nature - D configuration. Cyclic /Ring structure of monosaccharide环状半缩醛 Forma

6、tion of hemiacetals and hemiketals.Fisher projection formula to Haworth perspective formulas/异头物anomer,-变旋现象(mutarotation) D, L异头碳 Pyranose吡喃糖, Furanose呋喃糖5. The conformation of monosaccharide单糖的构象 Pyranose：Boat ChairConformation of furanose: Envelope form6. Monosaccharides Are Reducing Agentscan be

7、 oxidized by ferric (Fe3+) or cupric (Cu2+) ion. Reducing sugars Fehlings reaction葡萄糖酸内酯7. Important monosaccharides and derivativesSix carbon sugarProvide a rapid source of ATPPolymer form: Starch, cellulose-plants Glycogen-animalsFructose:ketohexose Free sugar in many fruits Derived from hydrolysi

8、s of sucroseGalactose Both the D and L forms are found in nature. Commonly found in milk as part of the disaccharide lactose L-Galactose is present in polysaccharides, such as agarDerivatives of monosaccharidesMonosaccharides can be chemically altered in several ways to provide new classes of compou

9、nds deoxy sugar 脱氧糖（羟基被氢原子取代） sugar acids 糖酸（醛基或伯醇基被氧化） alditols 糖醇（羰基被还原） amino sugars 氨基糖（分子中的一个羟基被氨 基取代） Sugar esters 糖脂（分子中的羟基与其他基团形成酯键） 岩藻糖 鼠李糖 6-脱氧-L-Gal 6-脱氧-L-Man 葡萄糖醛酸 葡萄糖酸 葡萄糖内酯uronic acid糖醛酸 aldonic acid醛糖酸 半乳糖胺 甘露糖胺Sugar EstersPhosphate esters are important metabolic intermediates：utilit

10、y, activityThe ribose moiety of nucleotides such as ATP is phosphorylated at the 5-position 8. Oligosaccharide Maltose 麦芽糖：reducing disaccharidesReducing endA product of starch degradationGlycosidic bondNomenclature of disaccharide. O-O-O-sucrose蔗糖：Glucose-fructoseNonreducing sugarsucroseformed by p

11、lants but not by animalsintermediate product of photosynthesisprincipal form in which sugar is transported from the leaves to other parts of the plant bodyhigh solubility Protective effects of most biomoleculesLactose 乳糖Galactose-glucoseLactoseoccurs naturally only in milk, 5% in milk, a reducing di

12、saccharide.Nutrition for infantsLactase and lactose intolerance9. 多糖 polysaccharidePolymers of monosaccharide units Homopolysaccharides同多糖 Heteropolysaccharides杂多糖DifferenceComopsition of the monomeric unitThe linkages between themThe ways in which branches from the chains occur. Storage polysacchar

13、ides: starch, glycogen Structural polysaccharides cellulose chitin Glycosaminoglycans 粘多糖 Proteoglycan蛋白聚糖 complex Bacterial cell wall amylose 直链淀粉 （14）GlucoseStarch淀粉 amylopectin 支链淀粉 （14）Glc （16）GlcGlycogen糖原:（14）and （16）Glcstarch store in cells with “granule”form淀粉颗粒The secondary structure of amy

14、lose: helixA cluster of amylose and amylopectin to occur in starch granules. Store in animal liver or muscle cells.GlycogenStructure of glycogenSimilar to that of amylopectinDifference: highly branched-why? chains are shorter more compactWhy not store glucose in its monomeric form? Cellulose 作为植物的骨架

15、-1,4-糖苷键目 录习题11Most animals cannot digest celluloseOnly ruminants 反刍动物 contain a symbiotic bacterium with cellulaseFungi too contain cellulaseN-acetyl-D-glucosamine, 1 4 bonds algae, fungi, arthropods（节肢动物）, mollusks（软体动物）, and insects.Chitin kaitin壳多糖Chitin is the second most abundant polysaccharid

16、e on earth.A beetleDextransbacterial and yeast polysaccharides made up of (1-6)-linked poly-D-glucose; have ( 1-3) branches, ( 1-2) or( 1-4) branches. Dental plaque, formed by bacteria growing on the surface of teeth, is rich in dextrans. Synthetic dextrans (Sephadex)- size-exclusion chromatography

17、Agaragaroseagar10. Heteropolysaccharides in bacterial cell wallsBacterial cell wallsGram-positive bacteria cross-linked multilayered peptideoglycan肽聚糖，layered on top of a lipid bilayer membranePeptides covalently link N-acetylmuramic acidThe mixture of L and D amino acids in the peptidesHave a penta

18、glycine chain in the cross-linkTeichoic acid 磷壁酸Eg. Sraphylococcus aureus 葡萄状球菌 penicillinpeptidoglycan组成肽聚糖的重复单元：Muropeptide胞壁肽 Oligopeptide: four residues NAG(GlcNAc) N-乙酰葡糖胺 Disaccharide NAM(MurNAc) N-乙酰胞壁酸Muropeptide 胞壁肽Gram-negative bacteriaA single layer of peptidoglycan sandwiched between out

19、er and inner lipid bilayer membranesLack the pentaglycineThe terminal D-Ala residue of one tetrapeptide is attached directly to a neighboring tetrapeptide through either L-Lys or a lysine-like amino acid脂多糖 Eg. Escherichia.coli11. Glycosaminoglycans 粘多糖，糖胺聚糖 -Heteropolysaccharides of the extracellul

20、ar matrix 软骨、腱等结缔组织中的结构多糖 糖醛酸己糖胺n n=30-250 uronic acid 糖醛酸Amine derivatives of hexoses 己糖胺The repeating unit carries a carboxyl group often one or more sulfates-acidicHave a high density of negative charges -extend conformation in solution.Often combined with protein to form proteoglycans-an importa

21、nt component of the extracelluar matrix of vertebratesGlycosaminoglycans functions:Extracellular matrix of skin and connective tissueViscosity Hydrophilic Lubrication in joints Anticoagulant 抗凝血剂hyaluronic acid contains alternating residues of D-glucuronic acid and N-acetylglucosamine.form clear, hi

22、ghly viscous solutions that serve as lubricants in the joints and eyes. an essential component of the extracellular matrix.Hyaluronidase- pathogenic bacteria infection sperm penetrating into ovum.Chondroitin 4-sulfate 硫酸软骨素Keratan sulfate硫酸角质素Heparin肝素 activate antithrombin-Anticoagulant 抗凝血One very

23、 long molecule of HAabout 100 molecules of the core protein aggrecanContains many covalently bound CS and KS chainsLink proteins mediate the core protein-HA interaction12. Proteoglycan aggregates蛋白聚糖Trisaccharide linker-connects a glycosaminoglycan to a Ser residue in the core proteinTrisaccharide l

24、inker整合素蛋白聚糖纤维连接蛋白纠结的胶原蛋白13. Cell identity: Lectin-OligosaccharidesOligosaccharides are enormously rich in structural information: 20 different subunits for construction of hexamer -oligonucleotides: 4,096 (46) -polypeptides: 6.4107 (206) -oligosaccharides: 1.441015 possibilitiessugar codereadable b

25、y the proteins thatinteract with it.Lectins Are Proteins That Read the Sugar Code and Mediate Many Biological ProcessesMovement of T lymphocytes to a site of inflammationSelectins are a family of plasma membrane lectinsP-selectin stored in the membranes of secretory granules.Whenendothelial cells ar

26、e activated by thrombin, P-selectin translocated to theplasma membrane.lectins mediate bacterial adhesion to host cells or toxin entry into cells.Eg：gastric ulcers胃溃疡 Helicobacter pylori幽门螺杆菌H.pylori has lectinsGastric epithelium has oligosaccharide LebLeb:part of type O blood group determinantUnderstanding the details of the oligosaccharide binding sites of lectins allows: a. drug development b. vaccine development L