Sephutheloana sa DNA ka har'a nucleus ea sele
Ka hare ho sele e 'ngoe le e 'ngoe ea eukaryotic—joalo ka ea batho, liphoofolo, limela le li-fungus—ho bolokiloe litaelo tsa bophelo ka mokhoa oa DNA (deoxyribonucleic acid). Haeba DNA e tsoang sele e le 'ngoe ea motho e ne e ka phutholoha, e ne e tla ba bolelele ba limithara tse ka bang peli. Phephetso: khoele e telele hakana e ka kena joang ka har'a nucleus ea sele, e bophara ba li-micrometer tse 'maloa feela, ntle le ho hokahana, e lula e sirelelitsoe, empa e ntse e fumaneha ha sele e hloka ho kopitsa kapa ho hlahisa liphatsa tsa lefutso? Karabo e lutse tsamaisong e hlophisitsoeng haholo le e matla ea ho paka DNA e tsejoang e le chromatin. Ho paka DNA ha se feela "ho mena" ha DNA; ke ts'ebetso ea baeloji e etsang qeto ea hore na liphatsa tsa lefutso li sebetsa kapa li khutsitse neng 'me li bapala karolo e kholo botsitsong ba genome.
DNA le bothata ba "sebaka" ka har'a nucleus
DNA ke polymer e telele e entsoeng ka li-nucleotide tse nang le metheo e mene e meholo: A, T, C, le G. Ho batho, DNA eohle e ka har'a nucleus ea sele e le 'ngoe e fihla ho lipara tse ka bang limilione tse likete tse 3 tsa motheo. Ka bolelele bona bo sa tloaelehang, DNA e ke ke ea tloheloa hore e phaphamale ka bolokolohi ka har'a nucleus. Ntle le mathata a sebaka, DNA e tlameha ho sireletsoa tšenyong ea 'mele le ea lik'hemik'hale, 'me e tlameha ho hlophisoa e le hore likarolo tse itseng li ka baloa (ho ngoloa) ho RNA ha ho hlokahala. Ka hona, lisele li sebelisa liprotheine tse khethehileng ho "hlophisisa" DNA e le hore e be nyane, e be makhethe ebile e sebetse.
Chromatin: mofuta o hlophisitsoeng oa DNA
Ka hara nucleus, DNA ha e yo e le nngwe, empa e amahanya le diprotheine—haholo-holo di-histone—ho etsa motsoako o bitswang chromatin. Chromatin e fetoha ka matla: tlasa maemo a itseng, e ka phutholoha ho dumella dijini ho fihlellwa, mme tlasa maemo a mang, e ka tiisa ho boloka sebaka kapa ho thibela dijini ho sebetsa. Chromatin e boetse e theha motheo wa ho thehwa ha di-chromosome, tse bonahalang hantle nakong ya karohano ya sele (mitosis kapa meiosis).
Ka kakaretso, chromatin e ka aroloa ka mefuta e 'meli:
1. Euchromatin: sebopeho se hlephileng, ka kakaretso se ruile liphatsa tsa lefutso tse sebetsang, tse fumanehang habonolo mechineng ea ho ngola.
2. Heterochromatin: sebopeho se teteaneng, liphatsa tsa lefutso li atisa ho se sebetse, hangata li na le libaka tse pheta-phetoang 'me li bapala karolo botsitsong ba li-chromosome.
Phapang ena e bohlokoa hobane e bontša hore sephutheloana sa DNA se amana ka ho toba le taolo ea liphatsa tsa lefutso.
Nucleosome: yuniti ea motheo ea sephutheloana sa DNA
Mohato oa pele oa ho paka DNA ke ho thehoa ha li-nucleosome, tseo hangata li bapisoang le "li-bead holim'a khoele." Li-nucleosome li entsoe ka leqeba la DNA le ka etsang makhetlo a 1,65 ho potoloha motheo oa protheine ea histone. Motheo ona o entsoe ka li-histone tse robeli (li-octamite): likopi tse peli tsa li-histone H2A, H2B, H3, le H4 ka 'ngoe.
Pakeng tsa di-nucleosome ho na le dikarolo tsa DNA tse hokelang tse bitswang linker DNA. Mona, histone H1 hangata e sebetsa e le "clamp," e thusang ho tsitsisa khoele ya DNA le ho tshehetsa ho thehwa ha sebopeho sa chromatin e teteaneng. Ho thehwa ha di-nucleosome ho ka kgutsufatsa DNA haholo le ho e sireletsa tshenyong, kaha karolo e kgolo ya bokahodimo ba DNA e kwahetswe ke diprotheine.
Ho tloha ho li-nucleosome ho ea ho likhoele tse teteaneng tsa chromatin
Hang ha di-nucleosome di se di thehilwe, mohato o latelang ke mokgahlelo wa boemo bo hodimo. Di-nucleosome ha di a lekana feela empa di ka boela tsa etsa di-fiber tse nyane tsa chromatin. Ka dilemo tse ngata, mohlala wa kgale o ile wa fana ka maikutlo a di-fiber tsa 30-nm (ka mokgwa wa "solenoid" kapa "zigzag"), le hoja dipatlisiso tsa sejwalejwale di bontshitse hore sebopeho sa chromatin diseleng tse phelang se ka fetoha haholo mme ha se kamehla se etsang di-fiber tse tshwanang tsa 30-nm. Ho hlakile hore dikamano tsa di-nucleosome, karolo ya histone H1, le maemo a ionic ka hara nucleus di kenya letsoho ho bongata ba chromatin.
Ho feta moo, ho paka ha ho felle feela ho likhoele. Chromatin e boetse e etsa li-loop kapa "li-circle" tse hoketsoeng moralo oa protheine ea nyutlelie. Li-loop tsena li lumella ho hlophisoa ha libaka tsa genomic: liphatsa tsa lefutso tse hlokang ho ba mafolofolo li ka beoa libakeng tse mosa ho ngoloa ha mongolo, ha libaka tse hlokang ho khutsa li ka "phutheloa" ka thata haholoanyane.
Libaka le meralo ea 3D ea genome
Sephutheloana sa DNA sa sejoale-joale se utloisisoa e le tokisetso ea mahlakore a mararo (3D) ea genome ka har'a nucleus. Genome ha e hlophisitsoe ka mokhoa o sa reroang; e etsa libaka tse sebetsang. Khopolo e 'ngoe ea bohlokoa ke Libaka tse Amanang le Topologically (TADs), libaka tsa DNA tse atisang ho sebelisana khafetsa le libaka tse ka har'a sebaka se le seng ho feta le libaka tse ka ntle ho sona. Sebopeho sena se thusa ho netefatsa hore li-enhancer (li-enhancer tsa transcriptional) li buisana le li-promoter tse nepahetseng tsa liphatsa tsa lefutso, ka hona li laola tlhahiso ea liphatsa tsa lefutso hamolemo.
Ntle le li-TAD, ho boetse ho na le likarolo tsa A le B: karolo ea A e atisa ho ba le euchromatin e ngata le liphatsa tsa lefutso tse mafolofolo, ha karolo ea B e na le heterochromatin e ngata le liphatsa tsa lefutso tse sa sebetseng. Sena se fana ka maikutlo a hore ho paka DNA ha se feela taba ea ho khomarelana, empa hape ke taba ea ho arola "libaka" tsa mosebetsi ka har'a khubu.
Liphetoho tsa Histone le epigenetics
E 'ngoe ea likarolo tse khahlisang ka ho fetisisa tsa ho paka DNA ke karolo ea eona ho epigenetics, e leng taolo ea liphatsa tsa lefutso tse sa fetoleng tatellano ea motheo ea DNA. Mehatla ea histone (likarolo tsa histone tse hlahang ho tsoa ho nucleosome) li ka fetoloa ka mekhoa e fapaneng ea lik'hemik'hale, mohlala:
– Acetylation (ka kakaretso e etsa hore chromatin e bulehe haholoanyane mme e eketsa ts'ebetso ea liphatsa tsa lefutso)
– Methylation (tšusumetso e ka kenya tshebetsong kapa ya hatella dijini ho latela sebaka)
- Phosphorylation, ubiquitination, le tse ling
Liphetoho tsena li sebetsa joaloka "khoutu" e amang hore na chromatin e pakiloe ka thata hakae le hore na ke liprotheine life tse ka khomarelang ho DNA. Ntle le li-histone, DNA ka boeona e ka feta methylation (mohlala, cytosine maemong a CpG liphoofolong), e atisang ho amahanngoa le ho thibeloa ha tlhahiso ea liphatsa tsa lefutso.
Kaha epigenetics e ka fetoha ho latela ntshetsopele, tikoloho le maemo a sele, ho paka DNA le hona hoa ikamahanya le maemo. Sena se bohlokwa ho kgetholleng disele: disele tsohle tsa mmele ka kakaretso di na le DNA e tshwanang, empa disele tsa methapo le mesifa di a fapana ka lebaka la dipaterone tse fapaneng tsa ho paka le ho hlahisa dijini.
Ho paka DNA nakong ea karohano ea sele: li-chromosome
Ha lisele li kena mitosis, boemo ba ho kopana ha DNA bo eketseha haholo, bo etsa li-chromosome tse bonahalang tlas'a microscope. Sena sea hlokahala ho arola DNA ka nepo ho lisele tse peli tsa morali. Nakong ena, chromatin e ba nyane haholo, 'me liphatsa tsa lefutso tse ngata ha li hlahisoe. Liprotheine tse kang condensin li thusa ho theha le ho tsitsisa sebopeho sa chromosome se kopaneng. Kamora hore karohano e phethehe, li-chromosome li "khutlisa" ho khutlela ho chromatin ho lumella ts'ebetso e tloaelehileng ea sele.
Ke hobane'ng ha ho paka DNA ho le bohlokoa?
Ho paka DNA ka hara nucleus ya sele ho na le mesebetsi e mmalwa e meholo:
1. Bokgoni ba sebaka: DNA e telele haholo e ka bolokoa ka hara nucleus e nyane.
2. Tšireletso: chromatin e thusa ho sireletsa DNA tšenyong le ho robeha ha ketane.
3. Taolo ea liphatsa tsa lefutso: boemo ba bongata ba chromatin bo khetholla phihlello ea liphatsa tsa lefutso, ka hona bo susumetsa tlhahiso ea liphatsa tsa lefutso.
4. Ho ikatisa le ho lokisa DNA: sephutheloana se lokela ho buloa ka nakoana e le hore lienzyme tsa ho ikatisa le ho lokisa li ka sebetsa, ebe li kopanngoa hape.
5. Ho tsitsa ha chromosome: sebopeho sa heterochromatin le tlhophiso ea 3D li thusa ho boloka botšepehi ba genome, haholo-holo libakeng tse kang centromeres le telomeres.
Liphoso tse ka har'a sephutheloana sa DNA li ka ba le liphello tse tebileng. Litšitiso liprotheineng tsa histone, lienzymes tsa epigenetic, kapa liprotheine tse laolang meralo ea chromatin li ka baka tlhahiso e sa tloaelehang ea liphatsa tsa lefutso 'me li amahanngoa le mafu a fapaneng, ho kenyeletsoa kankere, mathata a nts'etsopele le mafu a methapo ea kutlo.
Ho koala
Ho paka ha DNA ka har'a nucleus ea sele ke mohlala o mong oa limakatso tsa tlhophiso ea baeloji: molek'hule e telele haholo ea tlhahisoleseling e hatelloa ka katleho ntle le ho lahleheloa ke bokhoni ba eona ba ho fihlelloa le ho laoloa. Ka ho thehoa ha nucleosome, ho hlophisoa ha faeba ea chromatin, ho thehoa ha loop le domain ea 3D, le taolo ea epigenetic ka liphetoho tsa histone le DNA, lisele li khona ho leka-lekanya litlhoko tse peli tse bonahalang li hanyetsana: ho kopanya DNA ha ka nako e ts'oanang ho nolofalletsa tlhahiso e nepahetseng ea liphatsa tsa lefutso. Ho utloisisa lits'ebetso tsena ha ho bohlokoa feela bakeng sa baeloji ea motheo empa hape ho bula tsela bakeng sa mekhoa ea phekolo ea bongaka, kaha mafu a mangata a simolohile mathateng a chromatin le taolo ea epigenetic.
