Tsarin Kwafi a Ilimin Halittar Kwayoyin Halitta
Kwafi wani muhimmin tsari ne a fannin ilmin kwayoyin halitta wanda ke haɗa bayanan kwayoyin halitta a cikin DNA tare da samar da kwayoyin RNA. Ta hanyar kwafi, ana "fassara" jerin nucleotide a cikin DNA zuwa RNA, wanda daga nan zai iya aiki a matsayin RNA na manzo (mRNA) don haɗa furotin, ko kuma a matsayin wasu RNA masu aiki kamar rRNA da tRNA. Wannan tsari muhimmin ɓangare ne na babban ka'idar ilmin halitta: DNA → RNA → Protein. Duk da yake yana iya yin kama da mai sauƙi, kwafi ya ƙunshi jerin matakai da aka tsara, enzymes daban-daban, da kuma tsauraran tsari don ƙwayoyin halitta su iya bayyana kwayoyin halitta daidai yadda ake buƙata.
Manufofin asali na kwafi
A cikin rubutun, ana amfani da zaren DNA ɗaya kawai a matsayin zaren samfuri. Enzyme na RNA polymerase yana karanta zaren samfuri daga 3' zuwa 5' kuma yana haɗa sabon RNA a cikin alkiblar 5' zuwa 3'. Jerin RNA da ya biyo baya yana dacewa da zaren samfurin DNA, tare da babban bambanci: RNA yana amfani da uracil na tushe (U) maimakon thymine (T). Don haka, idan A yana cikin DNA, U shine haɗin tushe a cikin RNA, kuma idan C yana nan, G shine haɗin tushe (kuma akasin haka).
Kwafi na iya faruwa a cikin nau'ikan kwayoyin halitta daban-daban. Kwayoyin halittar da ke samar da furotin suna samar da mRNA, yayin da wasu kwayoyin halitta na iya samar da RNA mara tsari wanda ba a fassara shi zuwa furotin ba amma yana da ayyuka na tsari da na tsari, kamar su rRNA (tubalan ginin ribosomal), tRNA (masu ɗaukar amino acid), snRNA (haɗin gwiwa), da nau'ikan miRNA/lncRNA daban-daban waɗanda ke daidaita bayyanar kwayoyin halitta.
Babban abubuwan da ke tattare da su da bambance-bambance tsakanin prokaryotes da eukaryotes
A cikin prokaryotes (misali, ƙwayoyin cuta), tsarin rubutun abu ne mai sauƙi. Gabaɗaya akwai babban RNA polymerase guda ɗaya, tare da taimakon sigma factor, wanda ke gane mai haɓaka. Bugu da ƙari, saboda ƙwayoyin cuta ba su da tsakiya, rubutun da fassara na iya faruwa a lokaci guda a wuraren da ke kusa.
Sabanin haka, a cikin eukaryotes (misali, mutane), rubutun ya fi rikitarwa. Akwai polymerases da yawa na RNA: RNA polymerase I (yana fassara wasu rRNAs), RNA polymerase II (yana fassara mRNAs da wasu snRNAs/miRNAs), da RNA polymerase III (yana fassara tRNAs da 5S rRNAs). Bugu da ƙari, an saka DNA na eukaryotic a cikin chromatin, don haka samun damar shiga kwayoyin halitta yana buƙatar ƙarin tsari, gami da gyaran histone, sake fasalin chromatin, da kuma abubuwan rubutu daban-daban na gabaɗaya da takamaiman.
Mataki na 1: Fara rubutawa
Farawa shine matakin farko lokacin da aka haɗa injinan rubutun bayanai a daidai wurin da ke kan DNA. Wannan tsari yana farawa da gane mai haɓaka bayanai, wani takamaiman jerin DNA daga sama zuwa ga kwayar halitta wanda ke ƙayyade wurin fara rubutun.
Farawa a cikin prokaryotes
A cikin ƙwayoyin cuta, abubuwan sigma suna taimaka wa RNA polymerase gane muhimman abubuwan haɓaka kamar akwatin Pribnow da akwatin 35. Bayan RNA polymerase ya haɗu da mai haɓaka, wani "rufe hadaddun" yana samar da tsari. DNA da ke kusa da wurin farawa sannan ya buɗe wani ɓangare, yana samar da "buɗaɗɗen hadaddun," yana ba da damar RNA polymerase ya fara haɗa nucleotides na RNA na farko.
Farawa a cikin eukaryotes
A cikin eukaryotes, farawa yana ƙunshe da sunadaran da yawa. A cikin kwayoyin halittar da RNA polymerase II ta rubuta, masu haɓaka galibi (kodayake ba koyaushe ba) suna ɗauke da abubuwa kamar akwatin TATA. Sunadaran TATA-binding (TBP), wani ɓangare na hadaddun TFIID, yana gane akwatin TATA kuma yana ɗaukar wasu abubuwan rubutu na gabaɗaya (TFIIA, TFIIB, TFIIE, TFIIF, da TFIIH) da kuma RNA polymerase II. Wannan hadaddun ana kiransa hadaddun kafin farawa.
TFIIH tana taka muhimmiyar rawa domin tana da sinadarin helicase (na kwantar da DNA) da kuma aikin kinase, wanda ke samar da sinadarin phosphorylation na CTD (C-terminal domain) na RNA polymerase II. CTD phosphorylation yana taimakawa RNA polymerase II "saki" daga mai haɓaka shi kuma ya shiga matakin tsawaitawa, yayin da kuma ke samar da dandamali ga sunadaran sarrafa RNA.
Mataki na 2: Tsawaita rubutun
Bayan farawa, RNA polymerase yana motsawa tare da samfurin DNA kuma yana tsawaita sarkar RNA. Ana ƙara nucleotides na RNA (ATP, UTP, GTP, CTP) ɗaya bayan ɗaya, yayin da nau'ikan tushe ke faruwa. A lokacin tsawaitawa, RNA polymerase yana samar da kumfa na rubutu inda DNA ke kwance na ɗan lokaci. Bayan polymerase, DNA yana kwancewa, yayin da sabon RNA da aka samar ya fita daga hadaddun enzyme.
Elongation kuma yana da iyakataccen tsarin gyarawa. Idan matsala ta faru, RNA polymerase na iya dakatarwa da gyara kuskuren ta hanyar yanke ƙarshen RNA mara kyau, sannan a ci gaba da haɗa shi.
A cikin eukaryotes, tsawaitawa sau da yawa yana tare da ƙarin tsari, kamar dakatar da RNA polymerase II kusa da mai haɓaka. Wannan dakatarwa yana da mahimmanci don daidaita tsarin kwayoyin halitta da kuma shirye-shiryen yin saurin rubutu lokacin da ƙwayar ta sami takamaiman sigina.
Mataki na 3: Dakatar da kwafin rubutu
Karewa tsari ne na dakatar da kwafi da kuma sakin RNA da RNA polymerase daga DNA.
Cirewar prokaryotes a cikin ƙwayoyin cuta
Akwai manyan hanyoyi guda biyu:
1. Karewa ta ciki (wanda ba shi da alaƙa da rho): DNA tana da jerin da ke samar da RNA mai arzikin GC wanda ke samar da tsarin gashin gashi, sannan sai jerin U mai arzikin. Hairpin yana sa RNA polymerase ya tsaya kuma haɗin RNA-DNA yana rauni don haka hadaddun ya rabu.
2. Karewar Rho-dependent: Protein rho (helicase) yana manne da RNA kuma yana motsawa bayansa har sai ya kai ga polymerase na RNA da aka dakatar, sannan ya saki RNA daga hadaddun rubutun.
Ƙarewa a cikin eukaryotes (RNA polymerase II)
A cikin kwayoyin halitta da yawa, RNA polymerase II yana wucewa da siginar polyadenylation (misali, AAUAAA a cikin RNA) sannan a raba shi da wani hadadden tsari. Bayan yankewa, ƙarewa na iya faruwa ta hanyar samfurin "torpedo" (enzyme exonuclease yana lalata sauran RNA kuma yana bin polymerase) ko samfurin canji mai rikitarwa. Karewa a cikin polymerases na RNA I da III yana da wata hanya daban, wacce ta fi takamaiman tsari.
Sarrafa RNA a cikin eukaryotes: daga pre-mRNA zuwa mRNA mai girma
Babban bambanci tsakanin prokaryotes da eukaryotes shine cewa dole ne a sarrafa mRNA na eukaryotic kafin a iya fassara shi. Wannan tsari yana faruwa tare da rubutun (tare da rubutun) kuma ya haɗa da:
1. Maƙallin murfi mai inci 5: Ƙara rukunin 7-methylguanosine zuwa ƙarshen inci 5. Murfin yana kare RNA daga lalacewa, yana taimakawa wajen fitar da shi zuwa cytoplasm, kuma yana da mahimmanci don fara fassara.
2. Haɗawa: Cire introns da haɗa exons ta hanyar spliceosome. Madadin haɗawa na iya samar da isoforms na furotin da yawa daga kwayar halitta guda ɗaya, wanda ke ƙara bambancin proteome.
3. Polyadenylation (wutsiyar poly-A): Ƙara wutsiyar poly-A zuwa ƙarshen 3'. Wannan wutsiyar tana ƙara kwanciyar hankali na mRNA, tana taimakawa wajen fitar da kaya, kuma tana shafar ingancin fassara.
Ba a fassara RNA mara sarrafawa (pre-mRNA) ba. Tsarin kula da inganci na ƙwayar halitta zai riƙe ko ya lalata RNA mai lahani.
Tsarin fassara bayanai: me yasa dukkan kwayoyin halitta ba sa aiki a kowane lokaci?
Rubutun bayanai shine babban wurin da ake kula da bayyanar kwayoyin halitta. Kwayoyin halitta suna tsara waɗanne kwayoyin halitta ne ke aiki, yadda ake rubuta su da ƙarfi, da kuma lokacin da ya kamata a dakatar da rubutun bayanai. Wannan ƙa'ida tana ba ƙwayoyin halitta damar mayar da martani ga canje-canjen muhalli, siginar hormones, damuwa, ko buƙatun ci gaba.
A cikin prokaryotes, tsari sau da yawa yana buƙatar operon, kamar lac operon, wanda ke kunna enzyme mai raba lactose kawai lokacin da lactose yake. Abubuwan da ke hanawa da kunna abubuwa na iya hana ko haɓaka ɗaukar RNA polymerase.
A cikin eukaryotes, tsari ya fi rikitarwa. Abubuwa kamar masu haɓaka da masu shiru na iya kasancewa nesa da mai haɓaka amma suna tasiri ga aikin rubutun bayanai ta hanyar naɗe DNA da hulɗar furotin. Bugu da ƙari, yanayin chromatin (misali, histone acetylation, wanda ke sa DNA ta zama "buɗe") yana ƙayyade ko kwayar halitta tana da sauƙin isa ga injunan rubutun bayanai.
Penutup
Tsarin rubutun bayanai shine ginshiƙin yadda ake bayyana bayanan kwayoyin halitta a cikin RNA, duka a matsayin matsakaici don haɗa furotin da kuma a matsayin kwayar halitta mai aiki wacce ke gudanar da ayyukan tsari da tsari. Wannan tsari yana faruwa ta manyan matakai guda uku - farawa, tsawaitawa, da ƙarewa - tare da bambance-bambancen sarkakiya tsakanin prokaryotes da eukaryotes. A cikin eukaryotes, rubutun bayanai yana da alaƙa da sarrafa RNA kamar ƙirƙirar murfin 5', haɗawa, da polyadenylation. Saboda rubutun bayanai yana ƙarƙashin ƙa'idodi masu ƙarfi, fahimtar wannan tsari yana da mahimmanci a fannoni daban-daban, daga ilimin kwayoyin halitta da fasahar kere-kere zuwa maganin kwayoyin halitta, gami da fahimtar cututtukan da suka shafi rashin lafiyar bayyanar kwayoyin halitta.
