TAQSIMSHAVII HUJAYRA

Dar organizmhoi serhujayra hujayraho makhsus gashtaand, yane har yaki onho sokht va vazifai khudro dorad. Davomnokii hayoti hujayraho vobasta ba ijroi vazifai khud muayyan megardad. Masalan, hujayrahoi asab va mushak badi ba okhir rasidani davrai inkishofi janin digar taqsim nameshavand.

Dar davomi tamomi hayoti organizm vazifai khudro ijro mekunand. Hujayrahoi digar boshand, chunonchi, hujayrahoi magzi ustukhon va pardai ruda badi ijroi vazifai khud nobud megardand. Binobar in, dar chunin boftaho, hujayraho payiham qobiliyati taqsimshavi dorand.

Ba hamin minvol, sikli hayoti hujayra vaqti muayyanro darbar girifta, az davrai paydo shudani on, ki dar natijai taqsimshavi rukh medihad, to mahv shudan yo taqsimshavii oyanda idoma meyobad. Dar in muddat hujayra mesabzad, inkishof meyobad va vazifai khudro dar hayoti boftaho va organizmhoi serhujayra ijro mekunad.

Dar baze boftaho (magzi ustukhon, pardai ruda va gayraho),ki hujayraho doimo taqsim meshavand, yak qismi sikli hayoti onho bo sikli mitoz barobar ast. Majmui ravandhoi paydarham va bo hamdigar aloqamandi davrai omodagii pesh az taqsimshavi va rafti mitozro, sikli mitozi menomand (rasmi 5.18). Az rasm dida meshavad, ki badi ba okhir rasidani mitoz, hujayra ba taqsimshavii nav omodagi mebinad va davrai interfaza meguzarad.

Davri tayyorii pesh az sintezi KDN ba harfi G1 (az anglisi gap – masofai bayni) ishora shudaast. Dar in davr dar hujayra KRN va safedaho paydo shuda, faoliyati fermenthoe, ki dar biosintezi KDN ishtirok mekunand, afzun megardad. Badi khotimai fazai G1, hujayra ba sintezi KDN shuru karda, duchand megardad (fazai S). Dar in faza du spirali kuhnai molekulai KDN az ham judo shuda, har yaki onho baroi paydo kardani zanjiri navi KDN chun qolab khidmat mekunand (rasmi 5.19).

Dar har dui in molekulahoi dukhtari yake az zanjir (tor)-i polinukleotidii kuhna va digare zanjiri nav ast. Dar jarayoni sintezi KDN baze guruhhoi fermentho ishtirok mekunand, ki yake az asositarini onho KDN polimeraza ast.

Duchandshavii molekulai KDN bo tavri khos amali shuda, ba sokhti duzanjirii molekula vobasta ast: sokhti molekulai nav purra ba sokhti molekulai kuhna monand ast va mohiyatu mazmuni asosii biologii on mahz dar hamin ast. Agar sokhtori molekulai KDN vayron shavad, dar natija mazmni ramzi genetiki tagyir yofta, nigohdorii akhbori irsi va ba nasl guzashtani alomathoi baroi organizm khos gayrimumkin megardad. Vale dar natijai tasiri omilhoi khimiyavi va fizikavi (nurhoi ultrabunafsh, nurhoi rentgeni, baland shudani harorat va gayra) sokhtori az nav sintezshudai molekulai KDN vayron meshavad.

In holatro fermenthoi makhsus metavonand bartaraf kunand, yane onho joi vayronshudai molekulai KDN-ro, ki bo qolabi (matritsa) muvofiq nestand «shinokhta», tajziya mekunand va bo nukletidhoi muvofiq purra menamoyand.

Davomoti sintezi KDN, yane fazai S-i sikli mitozi dar hujayraho yak khel nabuda, az chand daqiqa (dar bakteriyaho) to 6-12 soat (dar hujayrahoi shirkhuron)-ro dar bar megirad.

Dar natijai duchandshavii KDN dar har khromosoma miqdori KDN nisbat ba ogozi fazai S du barobar ziyod ast, ammo miqdori khromosomaho tagyir nameyoband.

Dar natijai ba okhir rasidani reduplikatsiyai KDN dastai khromosomahoi hujayra 2p 4s (rasmi 5.18) tashkil mekunad. Badi khotimai sintezi KDN, yane fazai S-i sikli mitozii taqsimshavii hujayra yakbora shuru nameshavad,  zero az vaqti ba okhir rasidani sintezi KDN to ogozi taqsimshavii mitozro davrai G2 tashkil medihad. Mahz dar hamin davra tayyori ba taqsimshavii mitozi ba okhir merasad. Baroi ba taqsimshavii mitozi shuru kardan, gayr az duchandshavi KDN boz duchandshavii sentriolaho, sintezi safedaho, ki az hisobi on torhoi akhromatini sokhta meshavand, zarur ast. Barobari khotima yoftani tashakkuli hujayra jam 126 shudani energiya dar shakli ATF lozim ast. Taqsimshavii mitozi az chor fazai payiham, yane az profaza, metafaza, anafaza va telofaza (rasmi 5.20 va 5.21) iborat ast.

Dar davrai profaza hajmi yadro kalon shuda, galizii shirai on kam va khromosomaho namoyon megardand, zero onho shakli spiralro girifta, du sentriola ba qutbho ravona meshavand. Dar natijai shakli spiralro paydo kardani khromosomaho imkoniyati nuskhabardorii akhbori genetiki az

KDN qat megardad va sintezi KRN ba okhir merasad. Dar bayni qutbho torhoi akhromatini qad kashida, sokhtore tashkil meyobad, ki ba qutbho kashish khurdani khromosomahoro tamin menamoyad. Dar okhiri profaza pardai yadro ba qismhoi khurd taqsim shuda, gushaki in hissacha ba ham mechaspand.

Dar natija hubobchahoi khurd ba vujud omada, hamchun vakuolaho ba turi endoplazmavi yakjoya meshavand

Dar muddati profaza pechutobi khromosomaho idoma meyobad va onho kutohu gafs meshavand. Badi hazm shudani pardai yadro khromosomaho dar sitoplazma ozod va betartib joy megirand.

Dar metafaza pechutobi khromosomaho bo nuqtai balandtarin merasad, onho kutoh meshavand, ba markazi hujayra harakat karda, dar masofahoi gunoguni qutbi joy meyoband.

Qismi sentromeriyai khromosomaho bo tartibi muayyan dar khati markazi voqe gashta, dushhoi khromosomahoi khohari ozodona dar sitoplazma joy dorand. Torhoi mitozi komilan tashkil yofta, az nakhhoe iborat megardand, ki qutbro ba markazi khromosoma payvastaand.

Dar metafaza ba nazar merasad, ki khromosoma az du khromatid iborat buda, onho faqat bo sentromera payvasa meboshand.

Dar anafaza sentromerai har khromosoma judo shuda, az hamin lahza khromatidhoi khohari, khromosomahoi mustaqili dukhtariro tashkil mekunand. Tori akhromatini (duk), ki bo sentromera payvast ast, khromosomahoro bo qutbhoi hujayra kashida, dushhoi khromosoma az pasi on ravon meshavand va shakli U-ro megirand.

Hamin tavr, dar anafaza khromatidhoi duchandshudai davrai interfaza khromosomahoi mustaqili khohariro tashkil karda, onho ba qutbhoi ba yakdigar muqobili hujayra kashida meshavand. Dar in vaqt dar hujayra du dastai diploidii khromosomaho mavjud ast. Davrai ba okhir rasidani mitozro telofaza darbar megirad. Dar fazai mazkur khromosomahoi ba qutbho jafsshuda ba shakli rishta meguzarand va nagz namudor meshavand. Az sokhtorhoi membranavii sitop-

lazma pardai yadro tashakkul meyobad. Dar hujayrai hayvonot sitoplazma ba rohi kashishkhuri ba du qismi sitoplazmavi taqsim meshavad, ki har yaki onho doroi miqdori dastai diploidii khromosomaho ast. Dar hujayrai rastani boshad, membranai sitoplazmavi az bayni hujayra paydo shuda, ba kanor meravad va hujayraro ba du qismi barobar judo mekunad. Badi paydo shudani membranai sitoplazmavii ufuqi dar hujayrai rastaniho devorai sellyulozagi tashakkul meyobad. Dar sikli hujayra mitoz davrai nisbatan kutoh buda, az 0,5 to 3 soat idoma meyobad.

Hujayratukhmi bordor (zigota) ba taqsimshavii mitozi shuru menamoyad. Hamai hujayrahoi dukhtarie, ki az vay bo rohi mitoz taqsim shudaand, dastai khromosomaho va genhoi yakkhela dorand. Pas, malum megardad, ki mitoz tarzi taqsimshavii aniqi hujayra buda, hangomi on mavodi genetiki dar bayni hujayrahoi dukhtari barobar taqsim meshavad.

Ahamiyati biologii mitoz. Sokhtori betagyir va faoliyati durusti har uzvu boftai organizmhoi serhujayra bo yakkhela budani mavodi genetiki dar naslho vobasta ast.

Mitoz ravandhoi muhimi faoliyati hayoti, masalan inkishofi janin, sabzish, barqarorshavii uzvho va boftaho, badi oseb didan va gayraro ijro mekunad. Hamchunin nigoh doshtani umumiyati sokhtori boftaho hangomi mahv shudani hujayrahoi onho (ivaz shudani eritrotsithoi murda, pustpardai rudaho va gayra) ba mitoz vobasta ast.

Savolho baroi sanjish:

1. Sikli hayotii hujayra chist?
2. Sikli mitozii hujayraro sharh dihed.
3. Sintezi KDN chi guna ba amal meoyad?
4. Mitozro sharh dihed.
5. Mafhumi mitozro muayyan karda, ahamiyati biologii onrofahmoned.
6. Mohiyat va mazmuni mitoz dar chist?

Istilohot:

1. Interfaza – davrai tayyorii hujayra ba taqsimshavi, ki asosi onro duchandshavii KND tashkil medihad.
2. Sikli hayotii hujayra – majmui ravandhoe, ki dar hujayra meguzarand.
3. Sikli mitozii hujayra – majmui ravandhoe, ki dar hujayra meguzarand, az jumla dar vaqti omodagi ba taqsimshavi va mitoz.
4. Tafriqashavi – ravandi makhsusgardii hujayra baroi ijroi vazifai muayyan, ki dar sintezi safedahoi alohida ishtirok mekunad.
5. Boftai ustuvor – boftae, ki baroi aksariyati hujayrahoi sikli hayotash ba mitozi barobar ast.
6. Boftahoi ehyoshuda – yak qismi hujayrahoi tafriqashuda, lekin vaqti lozim metavonand az sari nav dar sikli mitozi tafriqa shavand.
7. Boftahoi sabzanda – hujayrahoe, ki differensiatsiyai bargasht dar janin va avvali davrai badi janini nadoshta dar tamomi hayoti hujayrahoi organizmho vazifaro ijro mekunad.
8. Mitoz – shakli afzoishi hujayra, ki dar on qismho aniq va barobar dar hujayrahoi dukhtari taqsim meshavand.