Luokittelu
Acellinthehumanbodycontainsabout10pgofRNA(about7pgofDNA).ComparedwithDNA,RNAhasawidevarietyoftypes,smallermolecularweights,andlargechangesincontent.RNAcanbedividedintomessengerRNAandnon-codingRNAaccordingtoitsstructureandfunction.Non-codingRNAisdividedintonon-codinglargeRNAandnon-codingsmallRNA.Largenon-codingRNAincludesribosomalRNAandlongnon-codingRNA.Non-codingsmallRNAsincludetransferRNA,ribozymes,smallmoleculeRNAsandsoon.SmallRNA(20~300nt)includesmiRNA,SiRNA,piRNA ,scRNA, snRNA, snoRNA jne. Bakteereilla on myös pieni RNA (50-500 nt).
MessengerRNA
MessengerRNA(mRNA)wasfirstdiscoveredin1960.Itisresponsiblefortransmittinggeneticinformationanddirectlyguidingproteinsynthesisduringproteinsynthesis.Ithasthefollowingcharacteristics.
1. Alhainen pitoisuus, osuus 1-5 % solu-RNA:sta.
2.Therearemanytypes,upto105species.DifferentgenesexpressdifferentmRNAs.
3.Thelifespanisshort,anddifferentmRNAguidesthesynthesisofdifferentproteins,whichwillbedegradedaftercompletingthemission.Theaveragehalf-lifeofbacterialmRNAisabout1.5minutes.Thehalf-lifeofvertebratemRNAvariesgreatly,withanaverageofabout3hours.
4.LargedifferencesinlengthmammalianmRNAlengthis5×102~1×105ntthemRNAofprokaryotesandeukaryotesalthoughTherearedifferencesinstructure,butthesamefunction,theyaretemplatesforguidingproteinsynthesis.
TransferRNA
TransferRNA(tRNA) on vastuussa aminohappojen kuljettamisesta ja mRNA:n geneettisen koodin tulkinnasta proteiinisynteesin aikana. tRNA muodostaa 10–15 % solu-RNA:sta, joista suurin osa sijaitsee sytoplasmassa.
1. RNA:n primäärirakenne
Sillä on seuraavat ominaisuudet:
①Se on yksijuosteisen pienmolekyyli-RNA:n tyyppi, pituus73 ~ 95 nt (konsensussekvenssi76 nt), sedimentaatiokerroin4S.
②Se RNA, jossa on eniten emäksiä, sisältää 7–15 harvinaista emästä (15–20 % kaikista emäksistä), joka sijaitsee parittomalla alueella.
③5′-pääteemäspehmeä guaniini.
④3'päättyy CCA-sekvenssiin, jossa adenyylihappo pehmenee nimeltä A76, ja sen 3'-OH on aminohappoa sitova kohta.
2.tRNA:n toissijainen rakenne
About50%basepairing,formingafour-segmentdoublehelix,formingaclover-shapedstructurewithfiveunpairedsequences.Therearefourarmsandfourloopsinthisstructure:
①Aminoacidarms.
②Dihydrourasiili (DHUarm, Darm) ja dihydrourasiilirengas (DHUring, Dring), jolle on ominaista, että se sisältää dihydrourasiilia (DHU, D).
③Theanticodonarmandanticodonlooparecharacterizedbythefactthattheanticodonloopcontainsanticodons.The5'endoftheanticodonisconnectedtouridineacid,andthe3'endisconnectedtopurinenucleotides.TheTΨCarm(Tarm)andtheTΨCring(Ψring)arecharacterizedbytheTΨCringcontainingthymineribonucleotideT54pseudouridineΨ55cytidineC56.
④Extraloop3~21nt.
3. RNA:n tertiäärinen rakenne
ItisL-shaped,withtheaminoacidbindingsiteatoneend,theanticodonloopattheotherend,andtheDHUloopAlthoughtheandTΨCringsarelocatedonbothsidesinthesecondarystructure,theyareadjacentinthetertiarystructure.AlthoughthelengthandsequenceofvarioustRNAsarenotthesame,theirtertiarystructureissimilar,suggestingthatthetertiarystructureiscloselyrelatedtoitsfunction.
Ribosomaalinen RNA
Ribosomaalinen RNA(rRNA)andribosomalproteinformakindofnucleoproteinparticlescalledribosomes.Thereareabout15,000ribosomesinanE.coli.
1.Ribosomien koostumus ja rakenne
Theribosomesofprokaryotesandeukaryotesarecomposedofalargesubunitandasmallsubunit.BothsubunitsarecomposedofrRNAandribosomalprotein.Thesizeofribosomes,ribosomalsubunitsandrRNAisgenerallyexpressedbythesedimentationcoefficient.
2.Ribosomaalisen RNA:n ominaisuudet
(1) Korkea pitoisuus, rRNA on korkein RNA:n pitoisuus solussa, mikä muodostaa 80 % solun kokonaisRNA:sta ~ 85 %.
(2) Pitkä käyttöikä, hidas rRNA-päivitys ja pitkä käyttöikä.
(3)Therearefewtypes.Prokaryoteshave5S,16S,and23srRNAs,whichaccountfor66%ofthemassofribosomes(5Sand23SrRNAsaccountfor70%ofthelargeribosomalsubunits,and16SrRNAItaccountsfor60%ofthesmallribosomalsubunits);eukaryotesmainlyhave5S,5.8S,18S,28SrRNA,andasmallamountofmitochondrialrRNAandchloroplastrRNA.Escherichiacoli16SrRNAhasaconservedsequenceACCUCCUatthe3'end,whichcancomplementallybindtotheSDsequenceinthemRNA.5TwoconservedsequencesofSrRNAhavealsobeenidentified:
①CGAAC,whichcancomplementtheGTCGoftheTΨCloopoftRNA.
②GCGCCGAAUGGUAGUvoi olla23SrRNA:n komplementtisekvenssi.
3.Ribosomityypit
Prokaryoteshaveonlyonetypeofribosomes,whileeukaryoteshavethefollowingtypeslocatedindifferentpartsofthecell:ribosomes,Freeribosomes,endoplasmicreticulumribosomes(alsocalledattachmentribosomes),mitochondrialribosomesandchloroplastribosomes(plants).Freeribosomesandendoplasmicreticulumribosomesareactuallythesametypeofribosomes.TheyarelargerthanprokaryoticribosomesandcontainmorerRNAandprotein.Mitochondrialribosomesandchloroplastribosomesaresmallerthanprokaryoticribosomes.However,thebasicstructureandfunctionoftheseribosomesarethesame.
Ribotsyymi
WhenscientistsarestudyingRNApost-transcriptionalprocessing,theyhavefoundthatcertainRNAshavecatalyticactivityandcancatalyzethesplicingofRNA.TheseRNAsaresynthesizedbylivingcellsandplayacatalyticrole.Knownasribozymes.ThesubstrateofmanyribozymesisalsoRNA,evenitsown,anditscatalyticreactionisalsospecific.
Thenaturalribozymesthathavebeenelucidatedincludehammerheadribozyme,hairpinribozyme,typeIintron,typeIIintron,hepatitisDvirusribozyme,ribonucleaseP,Peptidyltransferaseandsoon.Howtoevaluatethetheoreticalandpracticalsignificanceofribozymes,andhowtotreatthestatusofribozymesandtraditionalenzymesinmetabolism,allneedtobefurtherstudied.
1.Ribotsyymien löytäminen
RibotsyymiswerefirstdiscoveredbyCechandAltman(theNobelPrizewinnerinChemistryin1989).In1967,Woese,Crick,andOrgelproposedthatitmayhavecatalyticactivitybasedonthecomplexityoftheRNAsecondarystructure;in1982,Cechdiscoveredthatitsintronhasself-splicingactivitywhenstudyingthesplicingoftheTetrahymenarRNAprecursor;in1983,AltmanfoundthattheMRNAinribonucleasePisinvolvedinthepost-transcriptionalprocessingoftRNAprecursorswhenstudyingbacterialtRNAprecursors;in1982,Krugeretal.suggestedthatthecatalyticallyactiveRNAbenamed"ribozyme(ribozyme)".
2.Ribotsyymiominaisuudet
Thevariousribozymesdiscoveredsofarhavethefollowingcharacteristics.
(1)ThechemicalnatureofribozymesisRNAorRNAfragments.Someribonucleoproteinsalsohaveacatalyticeffect,buttheactivecenterislocatedontheirproteincomponentsandisnotaribozyme,suchastelomerase.However,iftheRNAoftheribonucleoproteincontainsanactivecenter,theRNAcomponentistheribozyme,suchastheM1RNAintheribonucleasePmolecule.
(2)Ribotsyymishaverelativelyfewtypesofsubstrates,mostofwhichareself-RNAorotherRNAmolecules.Therefore,theyaredividedintotwotypes:autocatalysisandheterocatalysis.Inaddition,thereareothersubstrates.Forexample,thesubstratesofpeptidyltransferaseareaminoacyltRNAandpeptidyltRNA.
(3)Thecatalyticefficiencyofribozymesismuchlowerthanthatofenzymes.
(4)Ribotsyymisarealsospecific.Forexample,M1RNAonlycutstheextranucleotidesatthe5'endoftheRNAprecursor,butdoesnotcuttheextranucleotidesandothersequencesatthe3'end.
(5)Thereactionscatalyzedbyribozymesareirreversible.
(6)Mg2+isrequiredfortheribozymetocatalyzethereaction.Mg3+notonlymaintainstheactiveconformationoftheribozyme,butalsoparticipatesinthecatalyticreaction.
(7)Solujen suurin osa ribotsyymeistä on erittäin alhainen.
3.Ribotsyymien merkitys
①ThediscoveryandresearchofribozymeshasgivenusafurtherunderstandingofthephysiologicalfunctionsofRNA,thatis,itisbothgeneticThecarrierofinformationisalsoabiocatalyst,whichhasthefunctionsoftwotypesofbiologicalmacromolecules,DNAandprotein.
②Ribotsyymien löytäminen vaikuttaa perinteiseen käsitykseen siitä, että kaikki biokatalyytit ovat proteiineja.
③Thediscoveryofribozymesisofgreatsignificanceforunderstandingtheevolutionoflife,andRNAmaybethefirstbiologicalmacromoleculetoappear.
4.Ribotsyymisovellus
①Geeniterapia;②Spesifinen RNA-hajoaminen;③Biosensori;④Funktionaalinen genomiikka;⑤Geenien löytäminen.
Jakelu soluissa
90%ofeukaryoticRNAisdistributedinthecytoplasm,andasmallamountisfoundinmitochondria,chloroplastsandnucleoli.
Prokaryoottien RNA on jakautunut sytoplasmaan.
Koostumusrakenne
LikeDNA,RNAisalsoapolynucleotidechaincomposedofvariousnucleotidesconnectedby3′,5′-phosphodiesterbonds,butwithDNAThereareaseriesofdifferences.
1.Intermsofchemicalcomposition,RNAcontainsribosebutnotdeoxyribose.Containsuracilbutdoesnotcontainthymidine.TheexceptionisthateachtNAmoleculecontainsathymine,whichismethylatedbyuracilaftertheRNAstrandissynthesized.Inaddition,asmentionedearlier,asmallnumberofDNAcontainsasmallamountofribose,buttheseindividualexceptionscannotbeusedThisnegatesthedifferenceinthecompositionofthetwotypesofnucleicacids.
2.AlthoughtheconceptofRNAprimarystructureisthesameasDNA.Butitsbasicstructuralunitisribonucleotideinsteadofdeoxyribonucleotide.Inaddition,partofRNAhasaspecialnucleotidesequenceatthe5'endor3'end,andthereisnocomplicatedsequenceorganizationlikeDNAintheRNAprimarystructure.
3.MostRNAsaresingle-strandedmolecules,whichcanfoldthemselvestoformahairpin-likestructureandhavethecharacteristicsofalocaldoublehelixstructure.ThisisthecommonfeatureofvariousRANspatialstructures.feature.TheruleofbasecomplementarypairinginthelocaldoublehelixstructureofRNAisAtoUandGtoC.SincethebasepairingcannotbefullyformedinsidetheRNAmolecule,thebasemolarratioAisnotequaltoU,GisnotequaltoC,andthereisnoChargafflawofDNAbaseratio.
Häiriömekanismi
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,andtheseinstructionsaretransmittedthroughmRNA.TheyfoundawaytodegrademRNAwithspecificgenes.InthisRNAinterferencephenomenon,double-strandedRNAinhibitsgeneexpressioninaveryclearway.Thistechnologyisusedinlaboratoriesaroundtheworldtodeterminewhichgenesplayanimportantroleinvariousdiseases.
RNAinterferenceexistsinplants,animals,andhumans,whichisofgreatsignificanceforthemanagementofgeneexpression,participationintheprotectionofviralinfections,andcontrolofactivegenes.RNAinterferenceisabiologicalprocessinwhichdouble-strandedRNAinhibitsgeneexpressioninaveryclearway.Sinceitsdiscoveryin1998,RNAinterferencehasemergedasapowerful"genesilencing"technology.RNAinterferencehasbeenwidelyusedinbasicscienceasaresearchmethodforstudyinggeneoperation,anditmayproducemorenewertreatmentmethodsinthefuture.ScientistsbelievethatRNAinterferencetechnologyisnotonlyapowerfultoolforstudyinggenefunctions.Inthenearfuture,thistechnologymaybeusedtodirectly“silence”disease-causinggenesfromthesourcetotreatcancerandevenAIDS.Itisalsousedinagriculture.Thereisalottobedone.
Toiminto
mRNA
mRNAcontainsfournucleotidesofA,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:⑨IntheentiremRNAmolecule,fromthestartsignaltothestopsignal,thetripletofthecodeiscontinuous,andthereisnointervalbetweenthecodeandthecode;②thestartsignalAUGisnotthestart(5'end)ofthemRNA,butcanbeseparatedfromthe5'endbyseveralnucleotides;andtheterminationsignalisnotatthe3'endofthemRNA.
tRNA
TherearemanykindsoftRNAsas"transportationtools".The20aminoacidsinthebodyhavetheirownuniquetRNAs.Therefore,therearenolessthan20typesoftRNAs.UndertheactionofATPtosupplyenergyandenzymes,tRNAcanbindtospecificaminoacidsrespectively.EachtRNAhasan"anti-code"madeupofthreenucleotides.Thisanti-codecanbepairedwiththecorrespondingcodeonthemRNAaccordingtotheprincipleofbasepairing,andonlywhentheanti-codecorrespondstothecodeonthemRNAcanitbematched,otherwiseitwillbe"outoffit".Therefore,duringtranslation,eachtRNAwithdifferentaminoacidscanbeaccurately"checked"onthemRNAmolecule,andinturnconformstothecanonicalcode,whichensuresthattheaminoacidscanbearrangedinacertainorder.
Ofcourse,theanti-codeonthetRNAshouldbeabletorecognizethecorrespondingandcomplementarycodeonthemRNAandpairwithit.However,whenexperimentingwithpurifiedtRNA,itwasfoundthatonetRNAcanrecognizeseveralcodes.Forexample,alaninetRNA,whoseanti-codeisIGC(5'>3'),canrecognizethreekindsofcodes.
rRNA
RRNAandavarietyofproteinmoleculestogetherformaribosome.Theribosomeisequivalenttoan"assemblymachine",whichcanpromotethecondensationofaminoacylgroupscarriedbytRNAintopeptides.TheribosomeattachestothemRNAandmovesalongthestartsignaltothestopsignalofthelongmRNAchain.AsforthespecificroleofrRNAinproteinbiosynthesis,itisunclear.