Primary structureProtein structureWhich of the following is not correct regarding secondary protein structureSecondary structurepolypeptides with similar sequences tend to adopt similar 3-dimensional structures and functions.protein conformation中文Which of the following is not correct regarding to protein tertiary and quaternary structureTertiary structure of proteinProtein primary structureProtein structure predictionQuaternary structureProtein quaternary structure

Protein Structure | Introduction to Chemistry - Lumen Learning

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Primary structure is the amino acid sequence. ... need to understand these four levels of protein structure: primary, secondary, tertiary, and quaternary. Skiptomaincontent IntroductiontoChemistry Polymers Searchfor: ProteinStructure   LearningObjective Summarizethefourlevelsofproteinstructure KeyPoints Proteinstructuredependsonitsaminoacidsequenceandlocal,low-energychemicalbondsbetweenatomsinboththepolypeptidebackboneandinaminoacidsidechains. Proteinstructureplaysakeyroleinitsfunction;ifaproteinlosesitsshapeatanystructurallevel,itmaynolongerbefunctional. Primarystructureistheaminoacidsequence. Secondarystructureislocalinteractionsbetweenstretchesofapolypeptidechainandincludesα-helixandβ-pleatedsheetstructures. Tertiarystructureistheoverallthethree-dimensionfoldingdrivenlargelybyinteractionsbetweenRgroups. Quarternarystructuresistheorientationandarrangementofsubunitsinamulti-subunitprotein. Terms β-pleatedsheetsecondarystructureofproteinswhereN-Hgroupsinthebackboneofonefully-extendedstrandestablishhydrogenbondswithC=Ogroupsinthebackboneofanadjacentfully-extendedstrand α-helixsecondarystructureofproteinswhereeverybackboneN-HcreatesahydrogenbondwiththeC=Ogroupoftheaminoacidfourresiduesearlierinthesamehelix. antiparallelThenatureoftheoppositeorientationsofthetwostrandsofDNAortwobetastrandsthatcompriseaprotein’ssecondarystructure disulfidebondAbond,consistingofacovalentbondbetweentwosulfuratoms,formedbythereactionoftwothiolgroups,especiallybetweenthethiolgroupsoftwoproteins Theshapeofaproteiniscriticaltoitsfunctionbecauseitdetermineswhethertheproteincaninteractwithothermolecules.Proteinstructuresareverycomplex,andresearchershaveonlyveryrecentlybeenabletoeasilyandquicklydeterminethestructureofcompleteproteinsdowntotheatomiclevel.(Thetechniquesuseddatebacktothe1950s,butuntilrecentlytheywereveryslowandlaborioustouse,socompleteproteinstructureswereveryslowtobesolved.)Earlystructuralbiochemistsconceptuallydividedproteinstructuresintofour“levels”tomakeiteasiertogetahandleonthecomplexityoftheoverallstructures.Todeterminehowtheproteingetsitsfinalshapeorconformation,weneedtounderstandthesefourlevelsofproteinstructure:primary,secondary,tertiary,andquaternary. PrimaryStructure Aprotein’sprimarystructureistheuniquesequenceofaminoacidsineachpolypeptidechainthatmakesuptheprotein.Really,thisisjustalistofwhichaminoacidsappearinwhichorderinapolypeptidechain,notreallyastructure.But,becausethefinalproteinstructureultimatelydependsonthissequence,thiswascalledtheprimarystructureofthepolypeptidechain.Forexample,thepancreatichormoneinsulinhastwopolypeptidechains,AandB. PrimarystructureTheAchainofinsulinis21aminoacidslongandtheBchainis30aminoacidslong,andeachsequenceisuniquetotheinsulinprotein. Thegene,orsequenceofDNA,ultimatelydeterminestheuniquesequenceofaminoacidsineachpeptidechain.Achangeinnucleotidesequenceofthegene’scodingregionmayleadtoadifferentaminoacidbeingaddedtothegrowingpolypeptidechain,causingachangeinproteinstructureandthereforefunction. Theoxygen-transportproteinhemoglobinconsistsoffourpolypeptidechains,twoidenticalαchainsandtwoidenticalβchains.Insicklecellanemia,asingleaminosubstitutioninthehemoglobinβchaincausesachangethestructureoftheentireprotein.Whentheaminoacidglutamicacidisreplacedbyvalineintheβchain,thepolypeptidefoldsintoanslightly-differentshapethatcreatesadysfunctionalhemoglobinprotein.So,justoneaminoacidsubstitutioncancausedramaticchanges.Thesedysfunctionalhemoglobinproteins,underlow-oxygenconditions,startassociatingwithoneanother,forminglongfibersmadefrommillionsofaggregatedhemoglobinsthatdistorttheredbloodcellsintocrescentor“sickle”shapes,whichclogarteries.Peopleaffectedbythediseaseoftenexperiencebreathlessness,dizziness,headaches,andabdominalpain. SicklecelldiseaseSicklecellsarecrescentshaped,whilenormalcellsaredisc-shaped. SecondaryStructure Aprotein’ssecondarystructureiswhateverregularstructuresarisefrominteractionsbetweenneighboringornear-byaminoacidsasthepolypeptidestartstofoldintoitsfunctionalthree-dimensionalform.SecondarystructuresariseasHbondsformbetweenlocalgroupsofaminoacidsinaregionofthepolypeptidechain.Rarelydoesasinglesecondarystructureextendthroughoutthepolypeptidechain.Itisusuallyjustinasectionofthechain.Themostcommonformsofsecondarystructurearetheα-helixandβ-pleatedsheetstructuresandtheyplayanimportantstructuralroleinmostglobularandfibrousproteins. SecondarystructureTheα-helixandβ-pleatedsheetformbecauseofhydrogenbondingbetweencarbonylandaminogroupsinthepeptidebackbone.Certainaminoacidshaveapropensitytoformanα-helix,whileothershaveapropensitytoformaβ-pleatedsheet. Intheα-helixchain,thehydrogenbondformsbetweentheoxygenatominthepolypeptidebackbonecarbonylgroupinoneaminoacidandthehydrogenatominthepolypeptidebackboneaminogroupofanotheraminoacidthatisfouraminoacidsfartheralongthechain.Thisholdsthestretchofaminoacidsinaright-handedcoil.Everyhelicalturninanalphahelixhas3.6aminoacidresidues.TheRgroups(thesidechains)ofthepolypeptideprotrudeoutfromtheα-helixchainandarenotinvolvedintheHbondsthatmaintaintheα-helixstructure. Inβ-pleatedsheets,stretchesofaminoacidsareheldinanalmostfully-extendedconformationthat“pleats”orzig-zagsduetothenon-linearnatureofsingleC-CandC-Ncovalentbonds.β-pleatedsheetsneveroccuralone.Theyhavetoheldinplacebyotherβ-pleatedsheets.Thestretchesofaminoacidsinβ-pleatedsheetsareheldintheirpleatedsheetstructurebecausehydrogenbondsformbetweentheoxygenatominapolypeptidebackbonecarbonylgroupofoneβ-pleatedsheetandthehydrogenatominapolypeptidebackboneaminogroupofanotherβ-pleatedsheet.Theβ-pleatedsheetswhichholdeachothertogetheralignparallelorantiparalleltoeachother.TheRgroupsoftheaminoacidsinaβ-pleatedsheetpointoutperpendiculartothehydrogenbondsholdingtheβ-pleatedsheetstogether,andarenotinvolvedinmaintainingtheβ-pleatedsheetstructure. TertiaryStructure Thetertiarystructureofapolypeptidechainisitsoverallthree-dimensionalshape,onceallthesecondarystructureelementshavefoldedtogetheramongeachother.Interactionsbetweenpolar,nonpolar,acidic,andbasicRgroupwithinthepolypeptidechaincreatethecomplexthree-dimensionaltertiarystructureofaprotein.Whenproteinfoldingtakesplaceintheaqueousenvironmentofthebody,thehydrophobicRgroupsofnonpolaraminoacidsmostlylieintheinterioroftheprotein,whilethehydrophilicRgroupsliemostlyontheoutside.Cysteinesidechainsformdisulfidelinkagesinthepresenceofoxygen,theonlycovalentbondformingduringproteinfolding.Alloftheseinteractions,weakandstrong,determinethefinalthree-dimensionalshapeoftheprotein.Whenaproteinlosesitsthree-dimensionalshape,itwillnolongerbefunctional. TertiarystructureThetertiarystructureofproteinsisdeterminedbyhydrophobicinteractions,ionicbonding,hydrogenbonding,anddisulfidelinkages. QuaternaryStructure Thequaternarystructureofaproteinishowitssubunitsareorientedandarrangedwithrespecttooneanother.Asaresult,quaternarystructureonlyappliestomulti-subunitproteins;thatis,proteinsmadefromonethanonepolypeptidechain.Proteinsmadefromasinglepolypeptidewillnothaveaquaternarystructure. Inproteinswithmorethanonesubunit,weakinteractionsbetweenthesubunitshelptostabilizetheoverallstructure.Enzymesoftenplaykeyrolesinbondingsubunitstoformthefinal,functioningprotein. Forexample,insulinisaball-shaped,globularproteinthatcontainsbothhydrogenbondsanddisulfidebondsthatholditstwopolypeptidechainstogether.Silkisafibrousproteinthatresultsfromhydrogenbondingbetweendifferentβ-pleatedchains. FourlevelsofproteinstructureThefourlevelsofproteinstructurecanbeobservedintheseillustrations.   ShowSources Boundlessvetsandcurateshigh-quality,openlylicensedcontentfromaroundtheInternet.Thisparticularresourceusedthefollowingsources: “Boundless.” http://www.boundless.com/ BoundlessLearning CCBY-SA3.0. “disulfidebond.” http://en.wiktionary.org/wiki/disulfide_bond Wiktionary CCBY-SA3.0. “hydrogenbond.” http://en.wiktionary.org/wiki/hydrogen_bond Wiktionary CCBY-SA3.0. “Boundless.” http://www.boundless.com//biology/definition/antiparallel BoundlessLearning CCBY-SA3.0. “OpenStaxCollege,Biology.October16,2013.” http://cnx.org/content/m44402/latest/?collection=col11448/latest OpenStaxCNX CCBY3.0. “OpenStaxCollege,Proteins.October16,2013.” http://cnx.org/content/m44402/latest/Figure_03_04_06.jpg OpenStaxCNX CCBY3.0. “OpenStaxCollege,Proteins.October16,2013.” http://cnx.org/content/m44402/latest/Figure_03_04_04.jpg OpenStaxCNX CCBY3.0. “OpenStaxCollege,Proteins.October16,2013.” http://cnx.org/content/m44402/latest/Figure_03_04_07.jpg OpenStaxCNX CCBY3.0. “OpenStaxCollege,Proteins.October16,2013.” http://cnx.org/content/m44402/latest/Figure_03_04_08.jpg OpenStaxCNX CCBY3.0. “OpenStaxCollege,Proteins.October16,2013.” http://cnx.org/content/m44402/latest/Figure_03_04_09.jpg OpenStaxCNX CCBY3.0. LicensesandAttributions CClicensedcontent,SharedpreviouslyBoundlessChemistry.Providedby:BoundlessLearning.Locatedat:https://www.boundless.com/chemistry/textbooks/boundless-chemistry-textbook/.License:CCBY-SA:Attribution-ShareAlike Previous Next

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