CHAPTER 3 Amino Acids and Peptides

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1、CHAPTER3:AminoAcids&PeptidesPeterJ.Kennelly;VictorW.RodwellINTRODUCTIONOBJECTIVESAfterstudyingthischapter,youshouldbeableto:Diagramthestructuresandwritethethree-andone-letterdesignationsforeachoftheaminoacidspresentinproteins.DescribethecontributionofeachtypeofRgroupoftheproteinaminoa

2、cidstotheirchemicalproperties.Listadditionalkeyfunctionsofaminoacidsandexplainhowcertainaminoacidsinplantseedscanseverelyimpacthumanhealth.NametheionizablegroupsoftheproteinaminoacidsandlisttheirapproximatepKavaluesasfreeaminoacidsinaqueoussolution.CalculatethepHofanunbufferedaqueous

3、solutionofapolyfunctionalaminoacidandthechangeinpHthatoccursfollowingtheadditionofagivenquantityofstrongacidoralkali.DefinepIandexplainitsrelationshiptothenetchargeonapolyfunctionalelectrolyte.ExplainhowpH,pKaandpIcanbeusedtopredictthemobilityofapolyelectrolyte,suchasanaminoacid,inadi

4、rect-currentelectricalfield.Describethedirectionality,nomenclature,andprimarystructureofpeptides.Describetheconformationalconsequencesofthepartialdouble-bondcharacterofthepeptidebondandidentifythebondsinthepeptidebackbonethatarefreetorotate.BIOMEDICALIMPORTANCEInadditiontoprovidingthe

5、monomerunitsfromwhichthelongpolypeptidechainsofproteinsaresynthesized,theL-α-aminoacidsandtheirderivativesparticipateincellularfunctionsasdiverseasnervetransmissionandthebiosynthesisofporphyrins,purines,pyrimidines,andurea.Theneuroendocrinesystememploysshortpolymersofaminoacidscalledpep

6、tidesashormones,hormone-releasingfactors,neuromodulators,andneurotransmitters.Humansandotherhigheranimalscannotsynthesize10oftheL-α-aminoacidspresentinproteinsinamountsadequatetosupportinfantgrowthortomaintainadulthealth.Consequently,thehumandietmustcontainadequatequantitiesofthesenutri

7、tionallyessentialaminoacids.Eachdaythekidneysfilterover50goffreeaminoacidsfromthearterialrenalblood.However,onlytracesoffreeaminoacidsnormallyappearintheurinebecauseaminoacidsarealmosttotallyreabsorbedintheproximaltubule,conservingthemforproteinsynthesisandothervitalfunctions.N