Ribonukleiinihappo

Thesynonymrnagenerallyreferstoribonucleicacid.

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.

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