Mitoza

Šema mitoze
Šema mitoze

Mitoza je dioba tjelesnih stanica, proces u kojem stanica udvostručuje svoj genom (genetski materijal) i zatim ga razdvaja u dvije istovjetne polovice. Nakon mitoze obično slijedi citokineza, u kojoj se cijela stanica dijeli na dvije približno jednake, genetski identične stanice-kćeri (klonove). Cijeli se proces naziva mitotska dioba.

Mitozom se dijele samo eukariotske stanice koje imaju jezgru, dok se prokarioti poput bakterija dijele binarnom fisijom.

Interfaza je faza životnog ciklusa stanice u kojoj se stanica priprema za mitozu.

Pet faza mitoze

  1. Profaza - počinje zgušnjavanjem i spiralizacijom kromatina u svrhu oblikovanja zbijenih kromosoma koji će se moći kretati u stanici bez međusobnog zaplitanja i lomova. Kromatin čija je DNK već upakirana u nukleosome, skraćuje se još oko 1000 puta i oblikuje kromosom (grč. khroma = boja; soma = tijelo). Skraćeni i zgusnuti kromosomi postaju vidljivi svjetlosnim mikrospokom. Sastoje se od dviju sestrnskih kromatida spojenih u poudručju centromera. Nestaje jezgrica i počinje oblikovanja diobenog vretena. U životinjskoj stanici centrosomi, udvostručeni u interfazi, putuju ne suprotne polove stanice, mikrotubuli se šire i oblikuju diobeni vreteno. U biljnoj stanici zbog nedostatka centrosoma, mikrotubuli staničnog skeleta preuređenjem oblikuju diobeno vreteno. Profaza završava razgradnjom jezgrine ovojnice čiji ostaci ostaju priljubljeni na oslobođenim kromosomima.
  2. Prometafaza - razdoblje kretanja kromosoma između središta i polova stanice. Na području centromera nalaze se specifični proteini koji oblikuju pričvrsnicu (kinetohoru), mjesto vezivanja niti diobenog vretena. Pričvrsnice su “molekularni motori” koji upravljaju kretanjem kromosoma duž vlakna vretena. Vezivanjem mikrotubula diobenog vretena na pričvrsnice kromosoma završava prometafaza i počinje metafaza.
  3. Metafaza - započinje završetkom prometafaze. Kromosomi kružno rasporede u sredinu diobenog vretena, u centar stanice koji se naziva matafazna ravnina. Raspad veza među sestrinskim kromatidama obilježava prijelaz u anafazu.
  4. Anafaza - započinje završetkom metafaze. Na početku anafaze kromatide se odvoje u području centromera, a kasnije potpuno, cijelom dužinom i od tog trenutka svaka kromatida je samostalni kromosom. Skaraćivanjem mikrotobula diobenog vretena kromosomi se kreću prema suprotnim polovima stanice.
  5. Telofaza - u posljednjoj fazi mitoze, telofazi kromosomi se na suprotnim polovima stanice “odmataju”, despiraliziraju i oblikuju kromatin. od dijelova stare jezgrine ovojnice, koje su kromosomi “donijeli” na polove, oblikuje se nova ovojnica. Događaji u telofazi vrlo su slični onima u profazi, samo se odvijaju obrnutim redosljedom. Po završetku telofaze stanica na polovima ima oblikovane dvije jednake jezgre čime je mitoza završena.

Galerija slika

Načini mitoze

Vanjske veze

U Wikimedijinoj ostavi nalazi se članak na temu: Mitoza
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