A DNA molecule yog ib qho qauv pom ntawm chromosome. Ib tug chromosome muaj ib tug xws li molecule uas muaj ob strands. DNA reduplication yog kev hloov pauv ntawm cov ntaub ntawv tom qab nws tus kheej tsim cov xov ntawm ib lub molecule mus rau lwm qhov. Nws muaj nyob hauv DNA thiab RNA. Kab lus no tham txog cov txheej txheem ntawm DNA reduplication.
Cov ntaub ntawv dav dav thiab hom DNA synthesis
Nws paub tias cov xov hauv cov molecule yog twisted. Txawm li cas los xij, thaum cov txheej txheem ntawm DNA reduplication pib, lawv despiralize, ces txav mus rau sab, thiab ib daim ntawv tshiab yog synthesized rau txhua. Tom qab ua tiav, ob qho tib si molecules tshwm sim, txhua tus muaj cov xov niam thiab tus ntxhais. Qhov no synthesis hu ua semi-conservative. DNA molecules txav mus deb, thaum tseem nyob hauv ib lub centromere, thiab thaum kawg diverge tsuas yog thaum lub centromere no pib faib.
Lwm hom kev sib txuas hu ua reparative. Nws, tsis zoo li yav dhau los,cuam tshuam nrog txhua theem cellular, tab sis pib thaum DNA puas tshwm sim. Yog hais tias lawv loj heev, ces lub cell nws thiaj li tuag. Txawm li cas los xij, yog tias qhov kev puas tsuaj nyob hauv cheeb tsam, ces nws tuaj yeem kho tau. Nyob ntawm qhov teeb meem, ib leeg lossis ob kab ntawm DNA yuav raug kho dua tshiab. Qhov no, raws li nws tseem hu ua, unscheduled synthesis tsis siv sij hawm ntev thiab tsis xav tau cov nqi zog loj.
Tab sis thaum DNA reduplication tshwm sim, ntau lub zog, khoom siv, nws lub sij hawm stretches rau teev.
Kev rov muab faib rau peb lub sijhawm:
- pib;
- elongation;
- kev txiav txim.
Cia peb saib kom ze ntawm qhov DNA rov ua ntu zus.
Kev pib
Muaj ntau kaum lab tus hauv paus khub hauv tib neeg DNA (tseem muaj ib puas thiab cuaj hauv tsiaj). DNA reduplication pib ntawm ntau qhov chaw hauv cov saw rau cov laj thawj hauv qab no. Nyob rau tib lub sijhawm, kev hloov pauv tshwm sim hauv RNA, tab sis nws raug tshem tawm hauv qee qhov chaw sib txawv thaum lub sijhawm DNA synthesis. Yog li ntawd, ua ntej xws li ib tug txheej txheem, ib tug txaus npaum li cas ntawm ib yam khoom accumulates nyob rau hauv lub cytoplasm ntawm lub cell thiaj li yuav tswj tau cov noob qhia thiab thiaj li hais tias lub cell qhov tseem ceeb kev ua ub no tsis cuam tshuam. Hauv kev pom ntawm qhov no, cov txheej txheem yuav tsum tau ua kom sai li sai tau. Kev tshaj tawm hauv lub sijhawm no tau ua tiav, thiab tsis muaj kev tshaj tawm. Cov kev tshawb fawb tau pom tias DNA reduplication tshwm sim ib zaug hauv ntau txhiab lub ntsiab lus - thaj chaw me me nrog qee qhovkev sib cais ntawm nucleotides. Lawv tau koom nrog cov protein tshwj xeeb pib, uas nyob rau hauv lem tau koom nrog lwm cov enzymes ntawm DNA replication.
Lub DNA tawg qhov twg kev sib txuas tshwm sim yog hu ua relicon. Nws pib los ntawm qhov pib taw tes thiab xaus thaum lub enzyme ua tiav replication. Lub relicon yog autonomous, thiab tseem muab tag nrho cov txheej txheem nrog nws tus kheej kev txhawb nqa.
txheej txheem yuav tsis pib los ntawm tag nrho cov ntsiab lus ib zaug, qhov chaw nws pib ua ntej, qhov chaw tom qab; tuaj yeem ntws hauv ib lossis ob qho kev taw qhia. Cov xwm txheej tshwm sim hauv qhov kev txiav txim hauv qab no thaum tsim tawm:
- replication fork;
- RNA primer.
Replication fork
Qhov no yog cov txheej txheem uas deoxyribonucleic strands tau ua ke ntawm cov kab sib txuas ntawm DNA. Cov diav rawg tsim lub npe hu ua reduplication eye. Cov txheej txheem yog ua ntej los ntawm kev ua:
- tso tawm los ntawm kev khi rau histones hauv nucleosome - DNA reduplication enzymes xws li methylation, acetylation thiab phosphorylation tsim cov tshuaj tiv thaiv uas ua rau cov proteins poob lawv cov nqi zoo, uas pab txhawb lawv tso tawm;
- kev ua siab phem yog qhov tsis txaus ntseeg uas tsim nyog los tso tawm cov xov ntxiv;
- tawg hydrogen bonds ntawm DNA strands;
- lawv kev sib txawv ntawm cov lus qhia sib txawv ntawm cov molecule;
- fixation by SSB proteins.
RNA primer
Synthesis ua tiavib qho enzyme hu ua DNA polymerase. Txawm li cas los xij, nws tsis tuaj yeem pib nws tus kheej, yog li lwm cov enzymes ua nws - RNA polymerases, uas tseem hu ua RNA primers. Lawv yog synthesized nyob rau hauv parallel nrog deoxyribonucleic strands raws li lub hauv paus ntsiab lus complementary. Yog li, qhov pib xaus nrog kev sib txuas ntawm ob lub RNA primers ntawm ob DNA strands uas tau tawg thiab muab tso rau hauv cov lus qhia sib txawv.
Kev sib tw
Lub sijhawm no pib nrog kev sib ntxiv ntawm nucleotide thiab 3' kawg ntawm RNA primer, uas yog ua los ntawm DNA polymerase uas twb tau hais lawm. Rau thawj, nws txuas qhov thib ob, thib peb nucleotide, thiab lwm yam. Cov hauv paus ntawm cov hlua tshiab txuas nrog cov niam txiv saw los ntawm hydrogen bonds. Nws ntseeg tau hais tias filament synthesis tshwm sim nyob rau hauv 5'-3' kev coj. Yog li ntawd, xws li xov yog hu ua coj los yog coj. RNA primers tsis tsim rau nws lawm.
Txawm li cas los xij, ntawm qhov sib txawv ntawm niam txiv strand, DNA nucleotides txuas ntxiv mus rau RNA primer, thiab cov saw deoxyribonucleic yog sib xyaw ua ke nyob rau hauv qhov sib txawv ntawm cov diav rawg rov qab. Hauv qhov no, nws yog hu ua lagging lossis lagging.
Ntawm lub lagging strand, synthesis tshwm sim fragmentarily, qhov twg, thaum kawg ntawm ib seem, synthesis pib ntawm lwm qhov chaw nyob ze siv tib RNA primer. Yog li, muaj ob qhov seem ntawm qhov lagging strand uas txuas nrog DNA thiab RNA. Lawv hu ua Okazaki fragments.
Tom qab ntawd txhua yam rov ua dua. Tom qab ntawd lwm tig ntawm lub helix unwinds, cov hydrogen bonds tawg, cov strands diverge mus rau sab, cov coj strand lengthens, lub tom ntej no fragment ntawm RNA primer yog synthesized ntawm lub lagging ib tug, tom qab uas lub Okazaki fragment. Tom qab ntawd, ntawm qhov lag luam strand, RNA primers raug rhuav tshem, thiab DNA tawg tau ua ke rau hauv ib qho. Yog li ntawm no Circuit Court tshwm sim ib txhij:
- tsim ntawm RNA primers tshiab;
- synthesis ntawm Okazaki fragments;
- kev puas tsuaj ntawm RNA primers;
- reunification into one one chain.
Kev txiav txim
Cov txheej txheem txuas ntxiv mus txog rau thaum ob qhov kev sib txuas ntawm rab rawg sib ntsib, lossis ib qho ntawm lawv mus txog qhov kawg ntawm cov molecule. Tom qab cov diav rawg sib ntsib, tus ntxhais strands ntawm DNA txuas nrog ib qho enzyme. Yog hais tias tus diav rawg tau txav mus rau qhov kawg ntawm cov molecule, DNA reduplication xaus nrog kev pab los ntawm tshwj xeeb enzymes.
Kho kom raug
Hauv cov txheej txheem no, lub luag haujlwm tseem ceeb tau muab rau kev tswj hwm (lossis kho) ntawm kev rov ua dua. Tag nrho plaub hom nucleotides tau nkag mus rau qhov chaw ntawm kev sib txuas, thiab los ntawm kev sim ua khub, DNA polymerase xaiv cov uas xav tau.
Qhov xav tau nucleotide yuav tsum muaj peev xwm tsim tau ntau li hydrogen bonds tib yam nucleotide ntawm DNA template strand. Tsis tas li ntawd, yuav tsum muaj qee qhov kev ncua deb ntawm cov qab zib-phosphate nraub qaum, sib xws rau peb lub nplhaib hauv ob lub hauv paus. Yog tias cov nucleotide tsis ua raws li cov kev cai no, kev sib txuas yuav tsis tshwm sim.
Kev tswj tau ua ntej nws suav nrog hauv cov saw thiab ua ntejsuav nrog cov nucleotide tom ntej. Tom qab ntawd, ib daim ntawv cog lus yog tsim nyob rau hauv lub caj qaum ntawm qab zib phosphate.
Kev hloov pauv hloov pauv
Lub tshuab ntawm DNA rov ua dua, txawm tias muaj feem pua ntawm qhov raug, ib txwm muaj kev cuam tshuam hauv cov xov, feem ntau hu ua "gene mutations". Kwv yees li ntawm ib txhiab lub hauv paus khub muaj ib qho yuam kev, uas yog hu ua convariant reduplication.
Nws tshwm sim rau ntau yam laj thawj. Piv txwv li, nyob rau hauv siab los yog tsawg heev concentration ntawm nucleotides, deamination ntawm cytosine, muaj mutagens nyob rau hauv lub synthesis cheeb tsam, thiab ntau dua. Qee qhov xwm txheej, kev ua yuam kev tuaj yeem raug kho los ntawm cov txheej txheem rov ua dua, hauv lwm qhov, kev kho yuav ua tsis tau.
Yog tias qhov kev puas tsuaj tau kov qhov chaw tsis muaj zog, qhov yuam kev yuav tsis muaj qhov tshwm sim loj thaum cov txheej txheem DNA rov ua dua. Cov nucleotide ib ntus ntawm ib lub noob yuav tshwm sim nrog qhov tsis sib xws. Tom qab ntawd qhov xwm txheej txawv, thiab ob qho tib si kev tuag ntawm lub xov tooj ntawm tes thiab kev tuag ntawm tag nrho cov kab mob tuaj yeem ua rau qhov tshwm sim tsis zoo. Nws tseem yuav tsum tau coj mus rau hauv tus account tias kev hloov pauv noob yog raws li kev hloov pauv hloov pauv, uas ua rau cov noob qoob loo ntau dua yas.
Methylation
Thaum lub sijhawm sib txuas lossis tam sim tom qab nws, cov saw methylation tshwm sim. Nws ntseeg tau tias hauv tib neeg, cov txheej txheem no yog qhov tsim nyog txhawm rau tsim cov chromosomes thiab tswj cov noob hloov pauv. Hauv cov kab mob, cov txheej txheem no ua haujlwm los tiv thaiv DNA los ntawm kev txiav los ntawm enzymes.
