Mekhoa ea ho Ngola Mangolo ho Biology ea Limolek'hule
Phetolelo ke ts'ebetso ea motheo baelojing ea limolek'hule e hokahanyang tlhahisoleseling ea liphatsa tsa lefutso ho DNA le tlhahiso ea limolek'hule tsa RNA. Ka phetolelo, tatellano ea nucleotide ho DNA e "fetoleloa" ho RNA, e ka sebetsang e le RNA ea moromuoa (mRNA) bakeng sa tlhahiso ea protheine, kapa e le li-RNA tse ling tse sebetsang joalo ka rRNA le tRNA. Ts'ebetso ena ke karolo ea bohlokoa ea thuto ea mantlha ea baeloji: DNA → RNA → Protheine. Le hoja e ka utloahala e le bonolo, phetolelo e kenyelletsa letoto la mehato e hlophisitsoeng, li-enzyme tse fapaneng, le taolo e tiileng e le hore lisele li ka hlahisa liphatsa tsa lefutso hantle kamoo ho hlokahalang.
Mehopolo ea motheo ea phetolelo
Mongolong, ke khoele e le 'ngoe feela ea DNA e sebelisoang e le khoele ea template. Enzyme ea RNA polymerase e bala khoele ea template ho tloha ho 3' ho isa ho 5' mme e kopanya RNA e ncha ka lehlakoreng la 5' ho isa ho 3'. Tatellano ea RNA e hlahang e tlatsana le khoele ea template ea DNA, ka phapang ea bohlokoa: RNA e sebelisa base uracil (U) ho fapana le thymine (T). Kahoo, haeba A e le teng ho DNA, U ke para ea motheo ho RNA, 'me haeba C e le teng, G ke para ea motheo (le ka tsela e fapaneng).
Phetolelo e ka etsahala mefuteng e fapaneng ea liphatsa tsa lefutso. Liphatsa tsa lefutso tse ngolang protheine li hlahisa mRNA, ha liphatsa tse ling tsa lefutso li ka hlahisa RNA e sa ngoleng khoutu e sa fetoleloang ho ba protheine empa e na le mesebetsi ea sebopeho le taolo, joalo ka rRNA (li-block tsa kaho ea ribosomal), tRNA (bajari ba amino acid), snRNA (splicing), le mefuta e fapaneng ea miRNA/lncRNA e laolang tlhahiso ea liphatsa tsa lefutso.
Likarolo tse ka sehloohong le liphapang lipakeng tsa prokaryotes le eukaryotes
Ho diprokaryote (mohlala, dibaktheria), tshebetso ya ho ngola e bonolo haholo. Ka kakaretso ho na le polymerase e le nngwe ya mantlha ya RNA, e thuswang ke sigma factor, e lemohang mohlohlelletsi. Ho feta moo, hobane dibaktheria ha di na nucleus, ho ngola le ho fetolela di ka etsahala ka nako e le nngwe dibakeng tse haufi.
Ka lehlakoreng le leng, ho li-eukaryote (mohlala, batho), phetolelo e rarahane haholo. Li-polymerase tse 'maloa tsa RNA li teng: RNA polymerase I (e ngola li-rRNA tse itseng), RNA polymerase II (e ngola li-mRNA le li-snRNA/miRNA tse ling), le RNA polymerase III (e ngola li-tRNA le li-rRNA tsa 5S). Ho feta moo, DNA ea eukaryotic e pakiloe ka har'a chromatin, kahoo phihlello ea liphatsa tsa lefutso e hloka taolo e eketsehileng, ho kenyeletsoa phetoho ea histone, ntlafatso ea chromatin, le lintlha tse fapaneng tsa phetolelo tse akaretsang le tse ikhethang.
Mokhahlelo oa 1: Ho qalisoa ha mongolo o ngotsoeng
Ho qala ke mohato wa pele ha mechini ya ho ngola e kopantswe sebakeng se nepahetseng ho DNA. Tshebetso ena e qala ka ho lemoha mohlohlelletsi, e leng tatellano e ikgethang ya DNA e nyolohang hodima jini e etsang qeto ya moo ho qalwang teng ho ngola.
Ho qalisoa ka har'a prokaryotes
Libaktheria, lintlha tsa sigma li thusa RNA polymerase ho lemoha likarolo tsa bohlokoa tsa promoter tse kang lebokose la Pribnow le lebokose la 35. Ka mor'a hore RNA polymerase e tlamelle ho promoter, ho thehoa "complex e koetsoeng". DNA e potolohileng moo ho qaloang teng e ntoo buleha hanyane, e etsa "complex e bulehileng," e lumellang RNA polymerase ho qala ho kopanya li-nucleotide tsa pele tsa RNA.
Ho qalisoa ha li-eukaryotes
Ho eukaryotes, ho qalisoa ho kenyelletsa liprotheine tse ngata. Liphatseng tsa lefutso tse fetisitsoeng ke RNA polymerase II, hangata li-promoter (leha e se kamehla) li na le likarolo tse kang lebokose la TATA. Protheine e tlamang TATA (TBP), karolo ea motsoako oa TFIID, e lemoha lebokose la TATA mme e sebelisa lintlha tse ling tse akaretsang tsa mongolo (TFIIA, TFIIB, TFIIIE, TFIIF, le TFIIH) hammoho le RNA polymerase II. Motsoako ona o bitsoa motsoako oa pele ho qalo.
TFIIH e bapala karolo ea bohlokoa hobane e na le helicase (DNA e lokollang) le ts'ebetso ea kinase, e fosforisang CTD (C-terminal domain) ea RNA polymerase II. Phosphorylation ea CTD e thusa RNA polymerase II ho "lokolla" ho tsoa ho promoter le ho kena mohatong oa ho lelefatsa, ha ka nako e ts'oanang e fana ka sethala sa liprotheine tse sebetsanang le RNA.
Mokhahlelo oa 2: Ho lelefatsa phetolelo
Kamora ho qalisoa, RNA polymerase e tsamaea ho latela mohlala oa DNA 'me e atolosa ketane ea RNA. Li-nucleotide tsa RNA (ATP, UTP, GTP, CTP) li eketsoa ka bonngoe, ha lipara tsa motheo li etsahala. Nakong ea ho atoloha, RNA polymerase e etsa bubble ea transcription moo DNA e phutholohang ka nakoana. Ka mor'a polymerase, DNA ea phutholoha, ha RNA e sa tsoa thehoa e tsoa mothating oa enzyme.
Ho lelefatsa le hona ho na le mokhoa o fokolang oa ho bala liphoso. Haeba ho hlaha phoso, RNA polymerase e ka emisa 'me ea lokisa phoso ka ho khaola ntlha e fosahetseng ea RNA, ebe e tsoela pele ho kopanya.
Ho li-eukaryote, ho lelefala hangata ho tsamaea le taolo e eketsehileng, joalo ka ho emisa RNA polymerase II haufi le promoter. Ho emisa hona ho bohlokoa bakeng sa taolo e hokahaneng ea liphatsa tsa lefutso le ho itokisetsa ho ngoloa ka potlako ha sele e amohela matšoao a itseng.
Mokhahlelo oa 3: Ho felisoa ha phetolelo
Ho fedisa ke tshebetso ya ho emisa ho ngolwa ha mongolo le ho lokolla RNA le RNA polymerase ho tswa ho DNA.
Ho fela ha prokaryotes
Ho na le mekhoa e 'meli e meholo:
1. Ho fela ha ka hare (ho sa itshetleheng ka rho): DNA e na le tatellano e hlahisang RNA e ruileng ka GC e etsang sebopeho sa hairpin, e latelwang ke tatellano e ruileng ka U. Hairpin e etsa hore RNA polymerase e eme mme tlamo ya RNA-DNA e fokole hoo motsoako o arohanang.
2. Ho fela ho itshetlehileng ka Rho: Protheine ya rho (helicase) e kgomarela RNA mme e tsamaya ka mora yona ho fihlela e fihla ho RNA polymerase e emisitsweng, ebe e lokolla RNA ho tswa ho transcription complex.
Ho fela ha li-eukaryote (RNA polymerase II)
Liphatseng tse ngata tsa lefutso, RNA polymerase II e fetisa lets'oao la polyadenylation (mohlala, AAUAAA ho RNA) ebe e aroloa ka mokhoa o sebetsang. Kamora ho aroloa, ho felisoa ho ka etsahala ka mohlala oa "torpedo" (enzyme ea exonuclease e senya RNA e setseng ebe e lelekisa polymerase) kapa mohlala o rarahaneng oa phetoho ea sebopeho. Ho felisoa ho RNA polymerases I le III ho na le mokhoa o fapaneng, o ikhethileng haholoanyane ka tatellano.
Ts'ebetso ea RNA ka har'a li-eukaryotes: ho tloha ho pre-mRNA ho ea ho mRNA e butsoitseng
Phapang e kgolo pakeng tsa di-prokaryotes le di-eukaryotes ke hore mRNA ya eukaryotic hangata e lokela ho sebetswa pele e ka fetolelwa. Tshebetso ena e etsahala ka ho ngolwa ha mongolo mmoho (hammoho le mongolo) mme e kenyeletsa:
Sehokelo sa sekoahelo sa 1. 5': Ho eketsa sehlopha sa 7-methylguanosine pheletsong ea 5'. Sehokelo se sireletsa RNA hore e se ke ea senyeha, se thusa ho romela cytoplasm, 'me se bohlokoa bakeng sa ho qalisoa ha phetolelo.
2. Ho kopanya: Ho tlosa di-intron le ho kopanya di-exons ke spliceosome. Ho kopanya ho hong ho ka hlahisa di-isoform tse ngata tsa protheine ho tswa ho jini e le nngwe, e leng se eketsang mefutafuta ya di-proteome.
3. Polyadenylation (mohatla oa poly-A): Ho eketsa mohatla oa poly-A pheletsong ea 3'. Mohatla ona o eketsa botsitso ba mRNA, o thusa ho romela kantle ho naha, 'me o ama katleho ea phetolelo.
RNA e sa sebetsoang (pre-mRNA) hangata ha e fetoleloe. Sistimi ea taolo ea boleng ea sele e tla boloka kapa e senye RNA e nang le sekoli.
Taolo ea phetolelo: ke hobane'ng ha liphatsa tsohle tsa lefutso li sa sebetse ka linako tsohle?
Phetolelo ke ntlha ea mantlha ea taolo bakeng sa tlhahiso ea liphatsa tsa lefutso. Lisele li laola hore na ke liphatsa life tsa lefutso tse sebetsang, hore na li ngotsoe ka matla hakae, le hore na phetolelo e lokela ho emisoa neng. Taolo ena e lumella lisele ho arabela liphetohong tsa tikoloho, matšoao a lihormone, khatello ea maikutlo, kapa litlhoko tsa nts'etsopele.
Ho prokaryotes, taolo hangata e kenyelletsa li-operon, tse kang lac operon, e kenyang tšebetsong enzyme e arolang lactose ha feela lactose e le teng. Lintho tse hatellang le tse susumetsang li ka thibela kapa tsa ntlafatsa ho hiroa ha RNA polymerase.
Ho eukaryotes, taolo e rarahane haholo. Dikarolo tse kang di-enhancer le di-silencer di ka ba hole le promoter empa di susumetsa mosebetsi wa transcription ka ho mena ha DNA le dikamano tsa protheine. Ho feta moo, maemo a chromatin (mohlala, histone acetylation, e etsang hore DNA e "bulehe" haholoanyane) a etsa qeto e kgolo ya hore na jini e ka fihlellwa ke mechini ya transcription.
Ho koala
Mokhoa oa ho ngola mongolo ke oona o ka sehloohong oa kamoo tlhahisoleseling ea liphatsa tsa lefutso e hlalosoang ka har'a RNA, e le mokhoa oa ho kopanya protheine le e le molek'hule o sebetsang o phethang mesebetsi ea taolo le ea sebopeho. Ts'ebetso ena e etsahala ka mekhahlelo e meraro e meholo - ho qala, ho lelefatsa le ho felisa - ka ho rarahana ho fapaneng pakeng tsa prokaryotes le eukaryotes. Ho eukaryotes, ho ngola mongolo ho kopantsoe ka thata le ts'ebetso ea RNA joalo ka ho thehoa ha 5' cap, ho kopanya le polyadenylation. Hobane ho ngola mongolo ho boetse ho laoloa haholo, ho utloisisa ts'ebetso ena ho bohlokoa masimong a fapaneng, ho tloha ho liphatsa tsa lefutso le theknoloji ea baeloji ho ea ho meriana ea limolek'hule, ho kenyeletsoa le ho utloisisa mafu a amanang le ho senyeha ha tlhahiso ea liphatsa tsa lefutso.
