Kurongedza DNA mu nucleus yesero
Mukati mesero rega rega re eukaryotic—senge revanhu, mhuka, zvirimwa, uye fungi—munochengeterwa mirairo yehupenyu muchimiro cheDNA (deoxyribonucleic acid). Dai DNA kubva musero rimwe chete remunhu ikavhurwa, yaizoreba mamita maviri. Dambudziko: tambo refu kudaro ingapinda sei munucleus yesero, ine dhayamita shoma chete, isina kusungwa, inoramba yakadzivirirwa, asi ichiri kuwanikwa kana sero richida kukopa kana kuratidza majini? Mhinduro iri muhurongwa hwekurongedza DNA hwakarongwa uye hune simba hunozivikanwa sechromatin. Kurongedza DNA hakusi kungo "petwa" kweDNA; inzira yehupenyu inosarudza kuti majini ari kushanda kana kuti akanyarara uye ine basa guru mukugadzikana kwemajini.
DNA nedambudziko re "nzvimbo" munucleus
DNA ipolymer refu inoumbwa nemanucleotide ane mabhesi mana makuru: A, T, C, uye G. Muvanhu, DNA yese iri munucleus yesero rimwe inosvika mabhiriyoni matatu emabhesi maviri. Nehurefu uhwu hunoshamisa, DNA haigone kusiiwa ichiyangarara zvakasununguka munucleus. Kunze kwezvinetso zvemuchadenga, DNA inofanirawo kudzivirirwa kubva mukukuvadzwa kwemuviri nemakemikari, uye inofanira kurongeka kuitira kuti zvimwe zvikamu zvigone kuverengwa (kunyorerwa) muRNA kana zvichidikanwa. Nokudaro, masero anoshandisa mapuroteni akakosha "kuronga" DNA kuitira kuti ive diki, yakachena, uye inoshanda.
Chromatin: chimiro chakarongeka cheDNA
Mukati menucleus, DNA haisi yega, asi inobatanidzwa nemapuroteni—kunyanya histones—kuumba chinhu chinonzi chromatin. Chromatin inoshanduka-shanduka: pasi pemamwe mamiriro ezvinhu, inogona kuzorora kuti majini asvike, uye pasi pemamwe mamiriro ezvinhu, inogona kusimba kuchengetedza nzvimbo kana kuita kuti majini asashande. Chromatin inoumbawo hwaro hwekuumbwa kwemachromosomes, ayo anoonekwa zvakajeka panguva yekupatsanurwa kwemasero (mitosis kana meiosis).
Kazhinji, chromatin inogona kukamurwa kuita mafomu maviri:
1. Euchromatin: chimiro chakasununguka, chinowanzova nemajini anoshanda, chinowanikwa nyore nyore nemuchina wekunyora.
2. Heterochromatin: chimiro chakasimba, majini anowanzova asina simba, anowanzova nenzvimbo dzinodzokororwa uye anoita basa mukugadzikana kwemakromosomu.
Musiyano uyu wakakosha nekuti unoratidza kuti kurongedza DNA kwakabatana zvakananga nekudzora majini.
Nucleosome: chinhu chikuru chekurongedza DNA
Danho rekutanga pakurongedza DNA kuumbwa kwemanucleosome, anowanzo fananidzwa ne "mabeads patambo." Manucleosomes ane DNA ronda rinotenderera kanenge 1,65 kutenderera pakati peprotein yehistone. Pakati apa pane mahistone masere (octamites): makopi maviri ehistones H2A, H2B, H3, uye H4.
Pakati pemanucleosome pane zvikamu zveDNA zvinobatanidza zvinonzi linker DNA. Pano, histone H1 inowanzo shanda se "clamp," ichibatsira kudzikamisa DNA coil uye kutsigira kuumbwa kwechimiro che chromatin chakasimba. Kuumbwa kweNucleosome kunogona kupfupisa DNA zvakanyanya uye kuidzivirira kubva mukukuvadzwa, sezvo chikamu chikuru cheDNA chakafukidzwa nemapuroteni.
Kubva ku nucleosomes kusvika ku denser chromatin fibers
Kana nucleosome dzangoumbwa, danho rinotevera nderekurongeka kwepamusoro. Nucleosomes hadzingogumiri pakurongeka asi dzinogonawo kuumba fiber dzakaoma dzechromatin. Kwemakore mazhinji, modhi yekare yairatidza fiber dze30-nm (mu "solenoid" kana "zigzag"), kunyangwe tsvakiridzo yemazuva ano yakaratidza kuti chimiro chechromatin mumasero mapenyu chinogona kuchinja zvakanyanya uye hachigarogadzira fiber dze30-nm dzakafanana. Zviri pachena kuti, kudyidzana kwepakati penucleosome, basa rehistone H1, uye mamiriro eionic munucleus zvinopa simba mu chromatin density.
Uyezve, kurongedza hakugumiri pafibers. Chromatin inogadzirawo maropu kana "madenderedzwa" akabatanidzwa ku nucleus protein framework. Maropu aya anobvumira kurongeka kwenzvimbo dze genomic: majini anoda kushanda anogona kuiswa munzvimbo dzinoenderana ne transcription, nepo nzvimbo dzinoda kunyarara dzinogona "kuiswa" zvakasimba.
Nzvimbo uye magadzirirwo e3D e genome
Kurongedza DNA kwemazuva ano kunonzwisiswa sekurongeka kwegenome ine mativi matatu (3D) mukati menucleus. Genome haina kurongeka zvisina tsarukano; inoumba nzvimbo dzinoshanda. Imwe pfungwa inokosha ndeyeTopologically Associated Domains (TADs), nzvimbo dzeDNA dzinowanzo sangana kakawanda nenzvimbo dziri munzvimbo imwe chete pane nenzvimbo dziri kunze kwayo. Maumbirwo aya anobatsira kuona kuti zvinosimudzira (zvinosimudzira zvinyorwa) zvinotaurirana nevanokurudzira majini akakodzera, nokudaro zvichidzora zviri nani kutaurwa kwemajini.
Pamusoro peTADs, kunewo zvikamu zveA neB: chikamu cheA chinowanzova chakapfuma mu euchromatin nemajini anoshanda, nepo chikamu cheB chiine heterochromatin nemajini asingashande. Izvi zvinoratidza kuti kurongedza DNA hakusi kwekungobatanidza chete, asiwo kupatsanura "nzvimbo" dzebasa mukati menucleus.
Kugadziriswa kweHistone uye epigenetics
Chimwe chezvinhu zvinonakidza pakurongedza DNA ibasa rayo mu epigenetics, iro riri kutonga majini asingachinje kurongeka kweDNA. Miswe yeHistone (zvikamu zvehistones zvinobuda munucleosome) zvinogona kugadziriswa zvakasiyana-siyana zvemakemikari, semuenzaniso:
- Acetylation (inowanzoita kuti chromatin ivhurike zvakanyanya uye inowedzera mashandiro emajini)
– Methylation (kukanganisa kunogona kumutsa kana kudzvinyirira majini zvichienderana nenzvimbo)
- Phosphorylation, ubiquitination, nezvimwewo
Kugadziriswa uku kunoshanda se "kodhi" inokanganisa kuti chromatin yakaputirwa zvakasimba sei uye kuti mapuroteni api anogona kubatana neDNA. Kuwedzera kumahistones, DNA pachayo inogona kuita methylation (semuenzaniso, cytosine mumamiriro eCpG mumhuka), iyo inowanzobatanidzwa nekudziviswa kwekutaura kwemajini.
Nekuti epigenetics inogona kuchinja zvichienderana nekukura, nharaunda, uye mamiriro emasero, kurongedza DNA kunochinjikawo. Izvi zvakakosha mukusiyanisa masero: masero ese emuviri anowanzova neDNA imwe chete, asi masero etsinga netsandanyama anosiyana nekuda kwemapatani akasiyana ekurongedza uye kutaura kwemajini.
Kurongedza DNA panguva yekupatsanurwa kwemasero: ma chromosomes
Kana masero apinda mu mitosis, huwandu hwekuumbwa kweDNA hunowedzera zvakanyanya, zvichiita kuti ma chromosomes aonekwe pasi pe microscope. Izvi zvinodiwa kuti DNA iparadzaniswe nemazvo mumasero maviri emwanasikana. Munguva iyi, chromatin inova diki kwazvo, uye majini mazhinji haabudiswi. Mapuroteni akadai se condensin anobatsira kuumba nekugadzirisa chimiro che chromosome yakakamurwa. Mushure mekunge kupatsanurwa kwapera, ma chromosomes "anodzokera" kuita chromatin kuti abvumire kushanda zvakanaka kwemasero.
Sei kurongedza DNA kuchikosha?
Kurongedza DNA mu cell nucleus kune mabasa makuru akati wandei:
1. Kushanda zvakanaka kwenzvimbo: DNA yakareba kwazvo inogona kuchengetwa muchikamu chidiki chenucleus.
2. Dziviriro: chromatin inobatsira kuchengetedza DNA kubva mukukuvadzwa uye kuputsika kwecheni.
3. Kudzora majini: huwandu hwechromatin density hunosarudza mukana wekuwana majini, nokudaro zvichikanganisa kuratidzwa kwemajini.
4. Kudzokorora uye kugadzirisa DNA: kurongedza kunofanirwa kukwanisa kuvhurwa kwenguva pfupi kuitira kuti ma enzymes ekukopa uye kugadzirisa agone kushanda, ozobatanidzwazve.
5. Kugadzikana kwechromosome: chimiro cheheterochromatin uye kurongeka kwe3D zvinobatsira kuchengetedza kusimba kwegenome, kunyanya munzvimbo dzakadai semacentromeres nematelomeres.
Zvikanganiso muDNA packaging zvinogona kuva nemigumisiro yakakomba. Kukanganiswa kwemapuroteni ehistone, maenzymes epigenetic, kana mapuroteni anodzora magadzirirwo echromatin kunogona kukonzera kusarongeka kwemajini uye kwakabatana nezvirwere zvakasiyana-siyana, zvinosanganisira kenza, matambudziko ekukura, uye zvirwere zvinoderedza mashandiro etsinga.
Penutup
Kuiswa kweDNA mumasero emasero muenzaniso mumwe wezvishamiso zvekurongeka kwezvipenyu: molekyuru yeruzivo yakareba kwazvo inomanikidzwa zvinobudirira pasina kurasikirwa nekugona kwayo kuwanikwa uye kudzorwa. Kuburikidza nekuumbwa kwe nucleosome, kurongeka kwe chromatin fiber, kuumbwa kwe loop uye 3D domain, uye epigenetic control kuburikidza nekuchinja kwe histone ne DNA, masero anokwanisa kuyera zvinodiwa zviviri zvinoita sekunge zvinopesana: kubatanidza DNA ukuwo zvichigonesa kutaura kwemajini kwakanyatsojeka. Kunzwisisa maitiro aya hakungokoshi chete kune basic biology asiwo kunovhura nzira yekurapa, sezvo zvirwere zvakawanda zvichibva mukusagadzikana kwe chromatin uye epigenetic regulation.
