RNA yog ib qho tseem ceeb ntawm cov molecular genetic mechanisms ntawm lub cell. Cov ntsiab lus ntawm ribonucleic acids yog ob peb feem pua ntawm nws qhov hnyav qhuav, thiab kwv yees li 3-5% ntawm cov nyiaj no poob rau ntawm tus xa xov RNA (mRNA), uas yog koom ncaj qha rau hauv cov protein synthesis, pab txhawb rau kev siv genome.
Lub mRNA molecule encodes cov amino acid sequence ntawm cov protein nyeem los ntawm cov noob. Yog li, matrix ribonucleic acid yog lwm yam hu ua ntaub ntawv (mRNA).
yam ntxwv dav dav
Zoo li txhua yam ribonucleic acids, tus xa xov RNA yog cov saw ntawm ribonucleotides (adenine, guanine, cytosine thiab uracil) txuas rau ib leeg los ntawm phosphodiester bonds. Feem ntau, mRNA tsuas muaj lub hauv paus qauv, tab sis qee zaum nws muaj cov qauv thib ob.
Muaj ntau txhiab tus mRNA hom nyob rau hauv ib lub xovtooj ntawm tes, txhua tus sawv cev los ntawm 10-15 molecules sib raug rau ib qhov chaw tshwj xeeb hauv DNA. mRNA muaj cov ntaub ntawv hais txog cov qauv ntawm ib lossis ntau duacov kab mob) proteins. Cov amino acid sequence yog nthuav tawm ua triplets ntawm thaj tsam coding ntawm mRNA molecule.
Lub luag haujlwm lom neeg
Lub luag haujlwm tseem ceeb ntawm tus xa xov RNA yog siv cov ntaub ntawv caj ces los ntawm kev hloov nws ntawm DNA mus rau qhov chaw ntawm cov protein synthesis. Hauv qhov no, mRNA ua ob txoj haujlwm:
- rewrites cov ntaub ntawv hais txog lub hauv paus qauv ntawm cov protein los ntawm lub genome, uas yog ua nyob rau hauv tus txheej txheem ntawm transcription;
- cuam tshuam nrog cov protein-synthesizing apparatus (ribosomes) raws li semantic matrix uas txiav txim siab cov amino acid sequence.
Qhov tseeb, kev sau ntawv yog kev sib txuas ntawm RNA, uas DNA ua raws li tus qauv. Txawm li cas los xij, tsuas yog nyob rau hauv rooj plaub ntawm tus xa xov RNA ua cov txheej txheem no muaj txiaj ntsig ntawm kev sau cov ntaub ntawv hais txog cov protein los ntawm cov noob.
Nws yog mRNA uas yog tus neeg nruab nrab tseem ceeb los ntawm txoj hauv kev los ntawm genotype mus rau phenotype (DNA-RNA-protein) tau ua.
Lub neej ntawm mRNA hauv ib lub cell
Tus tub txib RNA nyob hauv lub xovtooj ntawm lub sijhawm luv heev. Lub sijhawm muaj nyob ntawm ib lub molecule yog tus yam ntxwv los ntawm ob qhov tsis muaj:
- Ua haujlwm ib nrab-lub neej yog txiav txim siab los ntawm lub peev xwm ntawm mRNA los ua tus qauv thiab ntsuas los ntawm kev txo qis ntawm cov protein synthesized ib molecule. Hauv prokaryotes, daim duab no yog kwv yees li 2 feeb. Lub sijhawm no, tus nqi ntawm cov protein synthesized yog halved.
- Tshuaj ib nrab-lub neej yog txiav txim los ntawm kev txo cov tub txib RNA molecules muaj peev xwm ntawm hybridization(complementary compound) nrog DNA, uas qhia txog kev ncaj ncees ntawm cov qauv thawj.
Tshuaj ib nrab-lub neej feem ntau ntev dua li kev ua haujlwm ib nrab-lub neej, txij li thaum pib me ntsis degradation ntawm cov molecule (piv txwv li, ib qho kev tawg ntawm cov saw hlau ribonucleotide) tseem tsis tau tiv thaiv hybridization nrog DNA, tab sis twb tiv thaiv cov protein. synthesis.
Ib nrab-lub neej yog ib lub tswv yim kev txheeb cais, yog li qhov muaj nyob ntawm ib qho RNA molecule tuaj yeem siab dua lossis qis dua tus nqi no. Raws li qhov tshwm sim, qee qhov mRNAs muaj sijhawm los txhais ob peb zaug, thaum lwm tus raug degraded ua ntej kev sib txuas ntawm ib qho protein molecule tiav.
Hais txog kev degradation, eukaryotic mRNAs ruaj khov dua li cov prokaryotic (ib nrab-lub neej yog li 6 teev). Vim li no, lawv yooj yim dua los cais tawm ntawm lub xovtooj tsis zoo.
mRNA qauv
Nucleotide ib ntus ntawm tus xa xov RNA suav nrog cov cheeb tsam uas txhais lus, uas yog cov qauv ntawm cov protein tau encoded, thiab cov cheeb tsam uas tsis muaj ntaub ntawv, qhov sib txawv ntawm cov prokaryotes thiab eukaryotes.
cheeb tsam coding pib nrog qhov pib codon (AUG) thiab xaus nrog ib qho ntawm qhov xaus codons (UAG, UGA, UAA). Nyob ntawm seb hom cell (nuclear lossis prokaryotic), tus xa xov RNA tuaj yeem muaj ib lossis ntau thaj chaw txhais lus. Nyob rau hauv thawj rooj plaub, nws yog hu ua monocistronic, thiab nyob rau hauv lub thib ob - polycistronic. Cov tom kawg yog tus yam ntxwv tsuas yog rau cov kab mob thiab archaea.
Cov qauv ntawm cov qauv thiab kev ua haujlwm ntawm mRNA hauv prokaryotes
cov txheej txheem sau npe hauv prokaryotesthiab kev txhais lus tshwm sim ib txhij, yog li tus tub txib RNA tsuas muaj cov qauv tseem ceeb xwb. Ib yam li hauv eukaryotes, nws yog sawv cev los ntawm cov kab sib txuas ntawm ribonucleotides, uas muaj cov ntaub ntawv xov xwm thiab tsis-coding cheeb tsam.
Feem ntau mRNAs ntawm cov kab mob thiab archaea yog polycistronic (muaj ob peb coding cheeb tsam), uas yog vim lub peculiarity ntawm lub koom haum ntawm prokaryotic genome, uas muaj ib tug operon qauv. Qhov no txhais tau hais tias cov ntaub ntawv hais txog ntau cov proteins yog encoded nyob rau hauv ib tug DNA transcripton, uas yog tom qab kis mus rau RNA. Ib feem me me ntawm tus xa xov RNA yog monocistronic.
Cov cheeb tsam tsis tau txhais ntawm cov kab mob mRNA yog sawv cev los ntawm:
- tus thawj coj ua ntu zus (nyob ntawm 5'-kawg);
- trailer (los yog kawg) ib ntus (nyob ntawm 3`-kawg);
- untranslated intercistronic regions (spacers) - nyob nruab nrab ntawm cheeb tsam coding ntawm polycistronic RNA.
Qhov ntev ntawm intercistronic sequences tuaj yeem yog los ntawm 1-2 txog 30 nucleotides.
Eukaryotic mRNA
Eukaryotic mRNA ib txwm monocistronic thiab muaj cov txheej txheem ntau dua ntawm cov cheeb tsam tsis-coding uas suav nrog:
- cap;
- 5'-untranslated area (5'NTR);
- 3`-tsis tau txhais thaj chaw (3`NTR);
- polyadenyl tail.
Cov qauv dav dav ntawm tus xa xov RNA hauv eukaryotes tuaj yeem sawv cev uaschemes nrog cov nram qab no ib ntus ntawm cov ntsiab lus: cap, 5`-UTR, AUG, txhais cheeb tsam, nres codon, 3`UTR, poly-A-tail.
Nyob hauv eukaryotes, cov txheej txheem ntawm kev sau ntawv thiab kev txhais lus raug cais ob lub sijhawm thiab qhov chaw. Tus tub txib RNA tau txais lub kaus mom thiab lub ntsej muag polyadenyl thaum lub sijhawm loj hlob, uas yog hu ua kev ua haujlwm, thiab tom qab ntawd raug thauj los ntawm cov nucleus mus rau cytoplasm, qhov twg ribosomes yog concentrated. Kev ua haujlwm kuj txiav tawm cov intros uas tau pauv mus rau RNA los ntawm eukaryotic genome.
Qhov twg ribonucleic acids tau ua ke
Txhua hom RNA yog tsim los ntawm cov enzymes tshwj xeeb (RNA polymerases) raws li DNA. Raws li, qhov chaw ntawm cov txheej txheem no hauv cov hlwb prokaryotic thiab eukaryotic txawv.
Nyob rau hauv eukaryotes, transcription yog nqa tawm nyob rau hauv lub nucleus, nyob rau hauv uas DNA yog concentrated nyob rau hauv daim ntawv ntawm chromatin. Nyob rau tib lub sijhawm, pre-mRNA yog synthesized ua ntej, uas dhau los ntawm ntau qhov kev hloov kho thiab tsuas yog tom qab ntawd thauj mus rau cytoplasm.
Nyob rau hauv prokaryotes, qhov chaw uas ribonucleic acids yog synthesized yog thaj tsam ntawm lub cytoplasm ciam teb rau nucleoid. RNA-synthesizing enzymes cuam tshuam nrog despiralized loops ntawm cov kab mob chromatin.
Kev hloov pauv txoj cai
Kev sib txuas ntawm tus xa xov RNA yog ua raws li lub hauv paus ntsiab lus ntawm kev sib xyaw ntawm nucleic acids thiab yog ua los ntawm RNA polymerases uas ua rau lub kaw lus ntawm phosphodiester bond ntawm ribonucleoside triphosphates.
Nyob rau hauv prokaryotes, mRNA yog synthesized los ntawm tib enzyme li lwm homribonucleotides, thiab hauv eukaryotes los ntawm RNA polymerase II.
Kev txhais lus suav nrog 3 theem: pib, elongation thiab xaus. Thaum thawj theem, cov polymerase txuas mus rau tus txhawb nqa, ib qho chaw tshwj xeeb uas ua ntej cov txheej txheem coding. Nyob rau theem elongation, cov enzyme tsim RNA saw los ntawm kev ntxiv nucleotides rau cov saw uas cuam tshuam nrog cov qauv DNA saw.
