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1、ThewordproteinthatIproposetoyou...Iwouldwishtoderivefromproteios,becauseitappearstobetheprimitiveorprincipalsubstanceofanimalnutritionthatplantspreparefortheherbivores,andwhichthelatterthenfurnishtothecarnivores.-J.J.Berzelius,IettertoC.J.Mulder,1B3BAminoAcids,FeptidesoandProteins3.1A
2、minoAcids72acids,covalentlylinkedincharacteristiclinearse-quences.Becauseeachoftheseaminoacidshasaside3.2PeptidesandProteins82chainwithdistinctivechemicalproperties,thisgroupof3.3WorkingwithProteins8520precursormoleculesmayberegardedasthealphabetinwhichthelanguageofproteinstructureisw
3、ritten.3.4TheStructureofProteins:PrimaryStructure92Proteinsarefoundinawiderangeofsizes,fromrela-tivelysmallpeptideswithjustafewaminoacidresiduestohugepol}.'rnerswithmolecularweightsinthemillions.roteinsmediatevirtuallyeveryprocessthattakesWhatismostremarkableisthatcellscanproduceplace
4、inacell,exhibitinganalmostendlessdiversityproteinswithstrikingiydjfferentpropertiesandactivitiesoffunctions.Toexplorethemolecularmechanismofbyjoiningthesame20aminoacidsinmanydifferentcom-abiologicalprocess,abiochemistalmostinevitablystudiesbinationsandsequences.Fromthesebuildingblocks
5、dif-oneormoreproteins.Proteinsarethemostabundantbio-ferentorganismscanmakesuchwidelydiverseproductslogicalmacromolecules,occurringinallcellsandallpartsasenzyrnes,hormones,antibodies,transporters,muscleofcells.Proteinsalsooccuringreatvariety;thousandsofflbers,thelensproteinoftheeye,fea
6、thers,spiderwebs,differentkindsmaybefoundinasinglecell.Asthear-rhinoceroshorn,milkproteins,antibiotics,mushroompoi-bitersofmolecularfunction,proteinsarethemostimpor-sons,andmynadothersubstanceshavingdistinctbiologi-tantflnalproductsoftheinformationpathwaysdiscussedcalactivities{F'ig-.
7、3-f).Amongtheseproteinproducts,inPartIIIofthisbook.Proteinsarethemolecularinstru-theenz)'rnesarethemostvariedandspecialtzed.Virtuallymentsttroughwhichgeneticinformationisexpressed.allcelh:larreactionsarecatalyzedbyerzy'rnes.RelativelysimpiemonomericsubunitsprovidetheProteinstructurean
8、dfunc
