Chapter 18 carbohydrates.ppt

1、Chapter 18 Carbohydrates and Nucleic Acids 碳水化合物（糖）和核酸,Ref: Wade, chapter 23 曾昭琼，第19、20章,Carbohydrates（糖，碳水化合物）,Synthesized by plants using sunlight to convert CO2 and H2O to glucose（葡萄糖） and O2. Polymers include starch（淀粉） and cellulose（纤维素）. Starch is storage unit for solar energy（太阳能）. Most sugar

2、s have formula Cn(H2O)n, “hydrate of carbon.” （“碳的水合物”）,Polyhydroxyaldehydes (多羟基醛), Polyhydroxyketones (多羟基酮), Compounds that can be hydrolyzed to them (能水解得到多羟基醛或多羟基酮的化合物）,Modern Definition of Carbohydrates,葡萄糖(glucose)、果糖(fructose)、半乳糖(galactose) 蔗糖(sucrose)、麦芽糖(maltose)、乳糖(lactose) 淀粉(starch)、纤维

3、素(cellulose),Classification of Carbohydrates (23-2),Monosacharides （单糖）: simple sugar polyhydroxyaldehydes or aldoses, (glucose葡萄糖) polyhydroxyketones or ketoses, (fructose果糖) Disaccharides （二糖） can be hydrolyzed to two monosaccharides. 蔗糖(sucrose)、麦芽糖(maltose)、乳糖(lactose) Oligosaccharides （寡糖）: 310

4、 glucose units Polysaccharides （多糖） hydrolyze to many monosaccharide units. E.g., starch and cellulose have 1000 glucose units.,Monosaccharides单糖,Classified by: aldose (醛糖) or ketose (酮糖) number of carbons in chain: trioses; tetroses ; pentoses; hexoses; heptoses X(三, 四, 五, 六, 七)碳糖，丙(丁, 戊, 己, 庚)糖 co

5、nfiguration of chiral carbon farthest from the carbonyl group: D-, L-,Classification of Monosaccharides 23-3,glucose (葡萄糖), a D-aldohexose D-己醛糖,fructose (果糖), a D-ketohexose D-己酮糖,D and L Sugars,D sugars can be degraded to the dextrorotatory (+) form of glyceraldehyde (右旋甘油醛). L sugars can be degra

6、ded to the levorotatory (-) form of glyceraldehyde (左旋甘油醛).,Naturally occurring carbohydrates are all D-sugars.,D-甘油醛,D-赤藓糖,D-苏阿糖,Family tree of D-aldoses,ref: 图19-1 or figure 23-3,D-核糖,D-树胶糖 阿拉伯糖,D-木糖,D-异木糖,D-葡萄糖,D-甘露糖,D-半乳糖,2. Structures of monosaccharides,Relative configuration 相对构型,erythro- /thr

7、eo- 赤式/苏式,Absolute configuration 绝对构型,R- /S-,D- /L- ：,Open-chain structure 开链结构 Cyclic structure 环状结构(5, 6-),Erythro and Threo (赤式和苏式) 23-4,Terms used for diastereomers with two adjacent chiral Cs, without symmetric ends. For symmetric molecules, use meso or d,l.,Epimers （差向异构体）23-5,具有三个或三个以上手性中心的化合

8、物，若只有一个手性中心不同，其它都相同，则互称为差向异构体（epimers）,Find the C-2, C-3, C-4 epimers of glucose from figure 23-3.,开链D-葡萄糖(glucose)结构记忆方法,hemiacetal 半缩醛(酮),acetal 缩醛(酮),Review,The addition of alcohols to aldehydes and ketones: Formation of Acetals(缩醛（酮）) 18-18,Unstable,Formation of hemiacetal and acetal,Hemiacetal

9、半缩醛(酮),acetal 缩醛(酮),Review,Cyclic hemiacetal stable,Cyclic Structures of Monosaccharides -Hemiacetal（半缩醛） Formation 23-6,Haworth formulas,Haworth formulas,Chair conformation (OH on C1 axial),Chair conformation (all substituents equatorial),除1-位碳外，其它碳上的羟基及羟甲基均处在平伏键上。,D-葡萄糖 (glucose),Drawing cyclic mo

10、nosaccharides,平放; 把羰基碳放在最右侧; C5、C6折向后方；C4-C5键旋转120度, CH2OH朝上, C5上OH指向羰基; 成环; 把环中氧原子放在右后方。,b-D-glucose is the predominant form at equilibrium,-D-(+)-glucopyranose,-D - (+)-glucopyranose,trans-, -,cis-, -,Cyclic Structure for Fructose 果糖,Cyclic hemiacetal formed by reaction of C=O at C2 with -OH at C5

11、.,cyclic form D-fructofuranose D-呋喃果糖,D-fructose(果糖),Anomers 端基（差向）异构体,anomeric carbon 异头碳，端基碳,Mutarotation (变旋现象),Glucose also called dextrose(右旋糖), = +52.6,-: 36%,-: 64%.,If an aldose can form a five- or six-membered ring, it will exist predominantly as a cyclic hemiacetal,Six-membered rings are c

12、alled pyranoses (吡喃糖) Five-membered rings are called furanoses (呋喃糖),Summary for the cyclic structure of monosaccarids,b- sugar is the predominant form at equilibrium.,Haworth projections allow us to see the relative orientation of the OH groups in the ring., and b- sugar are anomers 端基差向异构体.,Mutaro

13、tation(变旋现象) is an important property of anomers.,-D-(+)-glucopyranose -D-(+)-吡喃葡萄糖, -D-(+)-glucopyranose -D-(+)-吡喃葡萄糖,-D-(+)-glucofuranose -D-(+)-呋喃葡萄糖, -D-(+)-glucofuranose -D-(+)-呋喃葡萄糖,3. Reactions of monosaccharides,The reactions of aldehydes and ketones; The reactions of alcohols,C=O, -OH,Malto

14、se 麦芽糖,Cellobiose 纤维二糖,Lactose 乳糖,Which is a nonreducing sugar?,6. Polysaccharides,cellulose（纤维素）,Polymer of D-glucose, found in plants. Mammals lack the -glycosidase enzyme.,Amylose直链淀粉,Soluble starch, polymer of D-glucose. Starch-iodide complex, deep blue.,Amylopectin支链淀粉,Branched, insoluble fract

15、ion of starch.,Chitin（甲壳质）,Polymer of N-acetylglucosamine. Exoskeleton of insects.,Blood type（血型） is determined by the nature of the sugar bound to the protein on the surface of red blood cells,7. Nuleic acids 核酸,核糖 ribose,脱氧核糖 deoxyribose,核糖核苷 ribonucleosides,脱氧核糖核苷 deoxyribonucleosides,常见碱基(base),脲嘧啶 uracil (U),胞嘧啶 cytosine (C),腺嘌呤 adenine (A),鸟嘌呤 guanine (G),胸腺嘧啶 thymine(T),在RNA中存在下列四种核苷,脲苷 胞苷 腺苷 鸟苷,规则：嘧啶的1位和嘌呤环的9位分别和核糖的苷羟基相连,核苷酸 ribonucleic acid,核苷的磷酸酯：核苷的3-位或5-位的羟基和磷酸结合,Structure of DNA,-D-2-deoxyribofuranose is the sugar. Heterocyclic bases are cytosine（胞嘧啶 ） thymine (胸腺嘧啶) ad