Класификација
Acellinthehumanbodycontainsabout10pgofRNA(about7pgofDNA).ComparedwithDNA,RNAhasawidevarietyoftypes,smallermolecularweights,andlargechangesincontent.RNAcanbedividedintomessengeрРНАandnon-codingRNAaccordingtoitsstructureandfunction.Non-codingRNAisdividedintonon-codinglargeRNAandnon-codingsmallRNA.Largenon-codingRNAincludesribosomalRNAandlongnon-codingRNA.Non-codingsmallRNAsincludetransfeрРНА,ribozymes,smallmoleculeRNAsandsoon.SmallRNA(20~300nt)includesmiRNA,SiRNA,piRNA ,сцРНА,снРНА,сноРНА, итд. Бактерије такође имају малу РНК (50~500нт).
МессенгерРНА
МессенгерРНА(мРНА)wasfirstdiscoveredin1960.Itisresponsiblefortransmittinggeneticinformationanddirectlyguidingproteinsynthesisduringproteinsynthesis.Ithasthefollowingcharacteristics.
1. Низак садржај, који обухвата 1% до 5% укупне ћелијске РНК.
2.Therearemanytypes,upto105species.DifferentgenesexpressdifferentмРНАs.
3.Thelifespanisshort,anddifferentмРНАguidesthesynthesisofdifferentproteins,whichwillbedegradedaftercompletingthemission.Theaveragehalf-lifeofbacterialмРНАisabout1.5minutes.Thehalf-lifeofvertebrateмРНАvariesgreatly,withanaverageofabout3hours.
4.LargedifferencesinlengthmammalianмРНАlengthis5×102~1×105nttheмРНАofprokaryotesandeukaryotesalthoughTherearedifferencesinstructure,butthesamefunction,theyaretemplatesforguidingproteinsynthesis.
ТрансферРНА
ТрансферРНА(тРНА) је одговорна за транспорт аминокиселина и тумачење мРНК генетског кода током синтезе протеина. тРНА чини 10% до 15% укупне ћелијске РНК, већину која се налази у цитоплазми.
1.Примарна структура РНК
Има следеће карактеристике:
①То је тип једноланчаног малог молекула РНК, дужина 73~95нт (консензусна секвенца76нт), коефицијент седиментације 4С.
②То је РНК са базама најтраженијих, која садржи 7-15 ретких база (који чине 15%-20% свих база), лоцирани у неупареној области.
③5′терминалбасеисофтенгуанине.
④3'завршетак ЦЦА секвенце, у којој се денилна киселина назива А76, и њено 3'-ОХ место везивања аминокиселина.
2.тРНАсекундарна структура
About50%basepairing,formingafour-segmentdoublehelix,formingaclover-shapedstructurewithfiveunpairedsequences.Therearefourarmsandfourloopsinthisstructure:
①Аминоацидармс.
②Дихидроурациларм(ДХУарм,Дарм)идихидроурацилринг(ДХУринг,Дринг),карактеристичан по томе што садржи дихидроурацил(ДХУ,Д).
③Theanticodonarmandanticodonlooparecharacterizedbythefactthattheanticodonloopcontainsanticodons.The5'endoftheanticodonisconnectedtouridineacid,andthe3'endisconnectedtopurinenucleotides.TheTΨCarm(Tarm)andtheTΨCring(Ψring)arecharacterizedbytheTΨCringcontainingthymineribonucleotideT54pseudouridineΨ55cytidineC56.
④Ектралооп3~21нт.
3.Терцијарна структура РНК
ItisL-shaped,withtheaminoacidbindingsiteatoneend,theanticodonloopattheotherend,andtheDHUloopAlthoughtheandTΨCringsarelocatedonbothsidesinthesecondarystructure,theyareadjacentinthetertiarystructure.AlthoughthelengthandsequenceofvariousтРНАsarenotthesame,theirtertiarystructureissimilar,suggestingthatthetertiarystructureiscloselyrelatedtoitsfunction.
РибосомалнаРНА
РибосомалнаРНА(рРНА)andribosomalproteinformakindofnucleoproteinparticlescalledribosomes.Thereareabout15,000ribosomesinanE.coli.
1.Састав и структура рибосома
Theribosomesofprokaryotesandeukaryotesarecomposedofalargesubunitandasmallsubunit.BothsubunitsarecomposedofрРНАandribosomalprotein.Thesizeofribosomes,ribosomalsubunitsandрРНАisgenerallyexpressedbythesedimentationcoefficient.
2.Карактеристике рибозомалне РНК
(1) Висок садржај, рРНА је највећи садржај РНК у ћелији, што чини 80% укупне РНК ћелије ~ 85%.
(2) Дуг животни век, споро ажурирање РНА и дуг животни век.
(3)Therearefewtypes.Prokaryoteshave5S,16S,and23sрРНАs,whichaccountfor66%ofthemassofribosomes(5Sand23SрРНАsaccountfor70%ofthelargeribosomalsubunits,and16SрРНАItaccountsfor60%ofthesmallribosomalsubunits);eukaryotesmainlyhave5S,5.8S,18S,28SрРНА,andasmallamountofmitochondrialрРНАandchloroplastрРНА.Escherichiacoli16SрРНАhasaconservedsequenceACCUCCUatthe3'end,whichcancomplementallybindtotheSDsequenceintheмРНА.5TwoconservedsequencesofSрРНАhavealsobeenidentified:
①CGAAC,whichcancomplementtheGTCGoftheTΨCloopofтРНА.
②ГЦГЦЦГААУГГУАГУ може бити комплементаран низу 23СрРНА.
3.Типесофрибосомес
Prokaryoteshaveonlyonetypeofribosomes,whileeukaryoteshavethefollowingtypeslocatedindifferentpartsofthecell:ribosomes,Freeribosomes,endoplasmicreticulumribosomes(alsocalledattachmentribosomes),mitochondrialribosomesandchloroplastribosomes(plants).Freeribosomesandendoplasmicreticulumribosomesareactuallythesametypeofribosomes.TheyarelargerthanprokaryoticribosomesandcontainmoreрРНАandprotein.Mitochondrialribosomesandchloroplastribosomesaresmallerthanprokaryoticribosomes.However,thebasicstructureandfunctionoftheseribosomesarethesame.
рибозим
WhenscientistsarestudyingRNApost-transcriptionalprocessing,theyhavefoundthatcertainRNAshavecatalyticactivityandcancatalyzethesplicingofRNA.TheseRNAsaresynthesizedbylivingcellsandplayacatalyticrole.Knownasribozymes.ThesubstrateofmanyribozymesisalsoRNA,evenitsown,anditscatalyticreactionisalsospecific.
Thenaturalribozymesthathavebeenelucidatedincludehammerheadribozyme,hairpinribozyme,typeIintron,typeIIintron,hepatitisDvirusribozyme,ribonucleaseP,Peptidyltransferaseandsoon.Howtoevaluatethetheoreticalandpracticalsignificanceofribozymes,andhowtotreatthestatusofribozymesandtraditionalenzymesinmetabolism,allneedtobefurtherstudied.
1.Дисцовериофрибозимес
рибозимswerefirstdiscoveredbyCechandAltman(theNobelPrizewinnerinChemistryin1989).In1967,Woese,Crick,andOrgelproposedthatitmayhavecatalyticactivitybasedonthecomplexityoftheRNAsecondarystructure;in1982,Cechdiscoveredthatitsintronhasself-splicingactivitywhenstudyingthesplicingoftheTetrahymenaрРНАprecursor;in1983,AltmanfoundthattheMRNAinribonucleasePisinvolvedinthepost-transcriptionalprocessingofтРНАprecursorswhenstudyingbacterialтРНАprecursors;in1982,Krugeretal.suggestedthatthecatalyticallyactiveRNAbenamed"ribozyme(ribozyme)".
2.Карактеристике рибозима
Thevariousribozymesdiscoveredsofarhavethefollowingcharacteristics.
(1)ThechemicalnatureofribozymesisRNAoрРНАfragments.Someribonucleoproteinsalsohaveacatalyticeffect,buttheactivecenterislocatedontheirproteincomponentsandisnotaribozyme,suchastelomerase.However,iftheRNAoftheribonucleoproteincontainsanactivecenter,theRNAcomponentistheribozyme,suchastheM1RNAintheribonucleasePmolecule.
(2)рибозимshaverelativelyfewtypesofsubstrates,mostofwhichareself-RNAorotheрРНАmolecules.Therefore,theyaredividedintotwotypes:autocatalysisandheterocatalysis.Inaddition,thereareothersubstrates.Forexample,thesubstratesofpeptidyltransferaseareaminoacylтРНАandpeptidylтРНА.
(3)Thecatalyticefficiencyofribozymesismuchlowerthanthatofenzymes.
(4)рибозимsarealsospecific.Forexample,M1RNAonlycutstheextranucleotidesatthe5'endoftheRNAprecursor,butdoesnotcuttheextranucleotidesandothersequencesatthe3'end.
(5)Thereactionscatalyzedbyribozymesareirreversible.
(6)Mg2+isrequiredfortheribozymetocatalyzethereaction.Mg3+notonlymaintainstheactiveconformationoftheribozyme,butalsoparticipatesinthecatalyticreaction.
(7)Садржај мострибозима у ћелији је изузетно низак.
3.Сигнифицанцеофрибозимес
①ThediscoveryandresearchofribozymeshasgivenusafurtherunderstandingofthephysiologicalfunctionsofRNA,thatis,itisbothgeneticThecarrierofinformationisalsoabiocatalyst,whichhasthefunctionsoftwotypesofbiologicalmacromolecules,DNAandprotein.
②Откриће фрибозимес је уздрмало традиционални концепт да су сви биокатализатори протеини.
③Thediscoveryofribozymesisofgreatsignificanceforunderstandingtheevolutionoflife,andRNAmaybethefirstbiologicalmacromoleculetoappear.
4. Рибозимеапплицатион
①Генетерапија;②СпецифицРНАдеградација;③Биосензор;④Функционална геномика;⑤Генедисцовери.
Дистрибутионинцеллс
90%ofeukaryoticRNAisdistributedinthecytoplasm,andasmallamountisfoundinmitochondria,chloroplastsandnucleoli.
РНК прокариотезе је распоређена у цитоплазми.
Композицијаструктура
LikeDNA,RNAisalsoapolynucleotidechaincomposedofvariousnucleotidesconnectedby3′,5′-phosphodiesterbonds,butwithDNAThereareaseriesofdifferences.
1.Intermsofchemicalcomposition,RNAcontainsribosebutnotdeoxyribose.Containsuracilbutdoesnotcontainthymidine.TheexceptionisthateachtNAmoleculecontainsathymine,whichismethylatedbyuracilaftertheRNAstrandissynthesized.Inaddition,asmentionedearlier,asmallnumberofDNAcontainsasmallamountofribose,buttheseindividualexceptionscannotbeusedThisnegatesthedifferenceinthecompositionofthetwotypesofnucleicacids.
2.AlthoughtheconceptofRNAprimarystructureisthesameasDNA.Butitsbasicstructuralunitisribonucleotideinsteadofdeoxyribonucleotide.Inaddition,partofRNAhasaspecialnucleotidesequenceatthe5'endor3'end,andthereisnocomplicatedsequenceorganizationlikeDNAintheRNAprimarystructure.
3.MosтРНАsaresingle-strandedmolecules,whichcanfoldthemselvestoformahairpin-likestructureandhavethecharacteristicsofalocaldoublehelixstructure.ThisisthecommonfeatureofvariousRANspatialstructures.feature.TheruleofbasecomplementarypairinginthelocaldoublehelixstructureofRNAisAtoUandGtoC.SincethebasepairingcannotbefullyformedinsidetheRNAmolecule,thebasemolarratioAisnotequaltoU,GisnotequaltoC,andthereisnoChargafflawofDNAbaseratio.
Механизам интерференције
In1998,twoAmericanscientistsAndrewFallandCraigMellowjointlypublishedthediscoveryofRNA(ribonucleicacid)inthejournalNature.Thepaperontheinterferencemechanismiscalled"oneofthemostexcitingdiscoveriesinmolecularbiologyinrecenttimes"bycolleagues.
AndrewFarrwasborninSantaClaraCounty,California,USAin1959.HemajoredinmathematicsattheUniversityofCalifornia,Berkeley,andobtainedhisdegreeinjustthreeyears.In1983,hereceivedhisPh.D.degreeinbiologyfromMassachusettsInstituteofTechnology.Hegraduallybecameinterestedingeneticsinvolvingthemysteriesoflifeandregardeditashislifelongacademicpursuit.
CraigMellowwasbornin1960.Hisfatherwasapaleontologist.Duringhischildhood,MellowoftenfollowedhisfathertosearchforfossilsinthewesternUnitedStates.
Inthehighschoolera,Merlot'sinterestgraduallyshiftedtogeneticengineering.Atthattime,scientistsclonedthehumaninsulingeneandputitsDNA(deoxyribonucleicacid)intobacteria,sothataninfiniteamountofinsulincanbeartificiallysynthesized.Thisachievementhasbroughtgoodnewstomillionsofdiabeticpatientsworldwide.Melorecalled:"Scientificresearchcanreallyhaveanimpactonhumanhealth.Thisideaarousedmyinterest."
In1998,duringtheworkofFarrandMeloattheCarnegieInstitutionintheUnitedStates,TheycollaboratedtodiscoverthemechanismofRNAinterference.
AndrewFarrsaid:"TheworkofCraigandIistostudywhysomegenesstopfunctioning.Wetriedtocontrolthem.Wefoundsomethingthatcaneffectivelystopthem.Thesegenesdon’tIcan'ttellyouwhattheycando,soifyoucanstopthem,youcanstarttounderstandwhattheycando.However,itwasaChinesescholarwhofirstdiscoveredtheRNAphenomenon.Itisapitythathedidnotfurtherunderstandwhy."
Whattheydiscoveredwasakeymechanismforcontrollingtheflowofgeneticinformation.ThehumangenomesendsinstructionsforproteinproductionfromtheDNAinthenucleustotheproteinsynthesismechanism,andtheseinstructionsaretransmittedthroughмРНА.TheyfoundawaytodegradeмРНАwithspecificgenes.InthisRNAinterferencephenomenon,double-strandedRNAinhibitsgeneexpressioninaveryclearway.Thistechnologyisusedinlaboratoriesaroundtheworldtodeterminewhichgenesplayanimportantroleinvariousdiseases.
RNAinterferenceexistsinplants,animals,andhumans,whichisofgreatsignificanceforthemanagementofgeneexpression,participationintheprotectionofviralinfections,andcontrolofactivegenes.RNAinterferenceisabiologicalprocessinwhichdouble-strandedRNAinhibitsgeneexpressioninaveryclearway.Sinceitsdiscoveryin1998,RNAinterferencehasemergedasapowerful"genesilencing"technology.RNAinterferencehasbeenwidelyusedinbasicscienceasaresearchmethodforstudyinggeneoperation,anditmayproducemorenewertreatmentmethodsinthefuture.ScientistsbelievethaтРНАinterferencetechnologyisnotonlyapowerfultoolforstudyinggenefunctions.Inthenearfuture,thistechnologymaybeusedtodirectly“silence”disease-causinggenesfromthesourcetotreatcancerandevenAIDS.Itisalsousedinagriculture.Thereisalottobedone.
Функција
мРНА
мРНАcontainsfournucleotidesofA,U,G,andC,eachofwhichisconnectedtoformatriplet,namelyThecoderepresentstheinformationofanaminoacid,socalculatedaccordingtothepermutationandcombinationruleinmathematics,43=64differentcodescanbeformed.Accordingtotheexperimentalresults,thecorrespondingrelationshipbetween64codesandaminoacidsisdeducedasshowninthetablebelow.
Amongthe64codes,61codesrepresentvariousaminoacids.Thereisonlyonecodeforeachkindofaminoacid,andtherecanbe6more,but2and4arethemajority.Inaddition,thethreecodesUAA,UAG,andUGAaretheterminationsignalsforpeptidechainsynthesisanddonotrepresentanyaminoacids.Ineukaryotes,AUGisboththecodeformethionineandtheinitiationsignalforpeptidechainsynthesis.Inprokaryotes,GUG(thecodeforvalineineukaryotes)andAUGarebothItisthecodeofformylmethionineandthestartingphasenumberofpeptidechainsynthesis.Itcanbeseenthat,exceptGUG,allpasswordscanbeappliedfrombacteriatohigherorganisms,whichprovidesstrongevidenceforthetheoryofcommonoriginoforganisms.
Itmustbepointedout:⑨IntheentireмРНАmolecule,fromthestartsignaltothestopsignal,thetripletofthecodeiscontinuous,andthereisnointervalbetweenthecodeandthecode;②thestartsignalAUGisnotthestart(5'end)oftheмРНА,butcanbeseparatedfromthe5'endbyseveralnucleotides;andtheterminationsignalisnotatthe3'endoftheмРНА.
тРНА
TherearemanykindsofтРНАsas"transportationtools".The20aminoacidsinthebodyhavetheirownuniqueтРНАs.Therefore,therearenolessthan20typesofтРНАs.UndertheactionofATPtosupplyenergyandenzymes,тРНАcanbindtospecificaminoacidsrespectively.EachтРНАhasan"anti-code"madeupofthreenucleotides.Thisanti-codecanbepairedwiththecorrespondingcodeontheмРНАaccordingtotheprincipleofbasepairing,andonlywhentheanti-codecorrespondstothecodeontheмРНАcanitbematched,otherwiseitwillbe"outoffit".Therefore,duringtranslation,eachтРНАwithdifferentaminoacidscanbeaccurately"checked"ontheмРНАmolecule,andinturnconformstothecanonicalcode,whichensuresthattheaminoacidscanbearrangedinacertainorder.
Ofcourse,theanti-codeontheтРНАshouldbeabletorecognizethecorrespondingandcomplementarycodeontheмРНАandpairwithit.However,whenexperimentingwithpurifiedтРНА,itwasfoundthatoneтРНАcanrecognizeseveralcodes.Forexample,alanineтРНА,whoseanti-codeisIGC(5'>3'),canrecognizethreekindsofcodes.
рРНА
RRNAandavarietyofproteinmoleculestogetherformaribosome.Theribosomeisequivalenttoan"assemblymachine",whichcanpromotethecondensationofaminoacylgroupscarriedbyтРНАintopeptides.TheribosomeattachestotheмРНАandmovesalongthestartsignaltothestopsignalofthelongмРНАchain.AsforthespecificroleofрРНАinproteinbiosynthesis,itisunclear.