acids(氨基酸)

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1、Chapter19Biomolecules:AminoAcids,Peptides,andProteins19.1StructuresofAminoAcids19.2IsoelectricPoints19.3PeptidesandProteins19.4PeptideSynthesis19.5ClassificationofProteins19.6ProteinStructureAminoacids(氨基酸):Alanine(丙氨酸)Peptides(肽):ManyChainswithfewerthan50aminoacidsAmidebondsProte

2、in:(蛋白质)Forlargerchains19.1StructuresofAminoAcidsDipolarionZwitterion(偶极分子)Aminoacidsareamphoteric(两性离子):Inbasesolution:Inacidsolution:20α-aminocidsfoundinprotein.19ofthe20aminoacidsareprimaryamines;Proline(脯氨酸)isasecondaryamine.P476,Table15.1Differonlyinthenatureofsidechain.Glyci

3、ne(甘氨酸)(S)-AlanineL-Alanine(S)-PhenylalanineL-Phenylalanine(s)-SerineL-SerineL-Glycer-aldehydeAspaticacid(天冬氨酸)Glutamicacid(谷氨酸)AcidicLysine(赖氨酸)arginine(精氨酸)Histidine(组氨酸)basicTheothersareneutralaminoacids.19.2IsoelectricPoints(等电点)pHLowpH(protonated)HighpH(deprotonated)Isoelectr

4、icPoints(pI):AtsomeintermediatepH,theconcentrationofthedipolarionismaximal,theconcen-trationsoftheanionsandcationsareequal.pIpH=5.0~5.6Neutralaminoacid:acidicaminoacid:pIatlowerpHbasicaminoacid:pIathigherpHSeparationofamixtureofaminoacidsbyElectrophoresis(电泳).-+LysinepI=9.74Glycin

5、epI=5.97AsparticacidpI=2.77PaperstripatpH=5.97C-terminalAminoacidspolymerslinkedtogetherbyamidebonds.Peptidebond19.3PeptidesandProteinsAlainine(Ala)Serine(Ser)Alanylserine(Ala-Ser)(丙氨酰-丝氨酸)(丙-丝二肽)Dipeptide(二肽)Tripeptide(三肽)Proteins:MW:>10000N-terminal19.4PeptideSynthesisProtection

6、oftheaminogroupbyBOCgroup:Ex.:SynthesisofAlanine-Leucine:AlanineDi-tert-butyldicarbonateBoc-Ala2.Protectionofthecarboxylgroupbytreatmentwithmethanolorbenzylalcohol:BOCgroupcanberemovedbyCF3COOHThegroupscaneasilyberemovedbyNaOH(aq).3.ThetwoprotectedaminoacidsarecoupledusingDCC.Dicy

7、clohexylcarbodiimide(DCC)(二环己基碳二亚胺)4.RemovaloftheBOCgroup.5.Removalofestergroup.19.5ClassificationofProteins19.5.1.Classificationaccordingtothecomposition1.Simpleproteins:Bloodserumalbumin(血清蛋白),Globin(球蛋白).2.Conjugatedproteins(结合蛋白):Glycoprotein(糖蛋白),Hemoglobin(血红蛋白).19.5.2.Class

8、ificationaccordingtothethree-dime