Lub nucleus hauv eukaryotic cell yog lub hauv paus organelle uas ua haujlwm tseem ceeb thiab cov txheej txheem hluavtaws nyob ntawm. Ib feem tseem ceeb ntawm cov ntsiab lus ntawm lub nucleus yog sawv cev los ntawm filamentous DNA molecules ntawm ntau qib ntawm compaction ua ke nrog cov proteins. Cov no yog euchromatin (decondensed DNA) thiab heterochromatin (densely packed pieces of DNA).
Euchromatin ua lub luag haujlwm tseem ceeb hauv lub neej ntawm tes. Nws nyeem "kev qhia" rau kev sib dhos ntawm ribonucleic acid (RNA), uas dhau los ua lub hauv paus rau kev sib txuas ntawm polypeptide molecules.
Puas yog txhua tus muaj lub hauv paus?
Txhua tus muaj sia nyob, txij li qhov tsawg tshaj plaws mus rau qhov loj, tau muab cov ntaub ntawv caj ces hauv daim ntawv ntawm deoxyribonucleic acid. Muaj ob hom kev sib txawv ntawm qhov sawv cev hauv cov hlwb:
- Cov kab mob Prokaryotic (pre-nuclear) muaj cov hlwb uas tsis muaj kev sib cais. Lub chaw cia khoom ntawm lawv tsuas yog tsis muaj protein ntau-txheej ncig DNA tsuas yog ib thajcytoplasm hu ua nucleoid. Nucleic acid replication thiab protein synthesis tshwm sim nyob rau hauv prokaryotes nyob rau hauv ib tug cell chaw. Peb yuav tsis pom lawv ntawm qhov muag liab qab, vim tias cov neeg sawv cev ntawm pawg kab mob no yog cov kab mob microscopic, txog li 3 microns loj, kab mob.
- Eukaryotic kab mob yog tus cwj pwm los ntawm cov qauv cell complex, qhov twg cov ntaub ntawv keeb kwm raug tiv thaiv los ntawm ob daim nyias nyias ntawm lub nucleus. Linear DNA molecules, ua ke nrog histone proteins, tsim chromatin, uas nquag tsim RNA nrog kev pab los ntawm polyenzyme complexes. Protein synthesis tshwm sim hauv cytoplasm ntawm ribosomes.
Cov tsim nucleus hauv eukaryotic hlwb tuaj yeem pom thaum lub sijhawm sib cuam tshuam. Lub karyoplasm muaj cov pob txha protein (matrix), nucleoli thiab nucleoprotein complexes uas muaj cov seem ntawm heterochromatin thiab euchromatin. Lub xeev no ntawm lub nucleus txuas ntxiv mus txog thaum pib ntawm kev faib tawm ntawm tes, thaum daim nyias nyias thiab nucleoli ploj mus, thiab cov chromosomes tau txais cov duab zoo li tus pas nrig.
Lub hauv paus tseem ceeb
Lub ntsiab lus tseem ceeb ntawm cov ntsiab lus ntawm cov nucleus, chromatin, yog nws cov lus hais. Nws lub luag haujlwm suav nrog kev khaws cia, kev siv thiab xa cov ntaub ntawv caj ces txog lub xov tooj ntawm tes lossis kab mob. Qhov ncaj qha replicated ib feem ntawm chromatin yog euchromatin, uas nqa cov ntaub ntawv ntawm cov qauv ntawm cov proteins thiab ntau hom RNA.
Qhov seem ntawm lub nucleus ua haujlwm pabcuam, muab cov xwm txheej zoo rau kev siv cov ntaub ntawv caj ces:
- nucleoli -compacted thaj chaw ntawm cov ntsiab lus nuclear uas txiav txim siab qhov chaw rau kev sib txuas ntawm ribonucleic acids rau ribosomes;
- protein matrix npaj kev npaj ntawm chromosomes thiab tag nrho cov ntsiab lus ntawm nucleus, tswj nws cov duab;
- Lub semi-kua sab hauv ib puag ncig ntawm cov nucleus, karyoplasm, ua kom cov khoom thauj ntawm cov molecules thiab ntws ntawm ntau yam txheej txheem biochemical;
- Lub plhaub ob txheej ntawm lub nucleus, lub karyolemma, tiv thaiv cov khoom siv caj ces, muab kev xaiv ob sab ntawm cov molecules thiab molecular complexes vim complex nuclear pores.
Chromatin txhais li cas
Chromatin tau txais nws lub npe xyoo 1880 ua tsaug rau Flemming qhov kev sim ntawm kev soj ntsuam cov hlwb. Qhov tseeb yog tias thaum kho thiab staining, qee qhov ntawm lub xov tooj ntawm tes yog qhov tshwj xeeb tshaj yog pom zoo ("chromatin" txhais tau tias "stained"). Tom qab ntawd nws tau pom tias cov khoom no tau sawv cev los ntawm DNA nrog cov proteins, uas, vim nws cov kua qaub, ua kom pom cov alkaline dyes.
Stained chromosomes pom nyob rau hauv nruab nrab ntawm lub cell nyob rau hauv daim duab, tsim ib tug metaphase phaj.
Daim ntawv ntawm DNA muaj nyob
Hauv cov hlwb ntawm cov kab mob eukaryotic, cov nucleoprotein complexes ntawm chromatin tuaj yeem nyob hauv ob lub xeev.
- Nyob rau hauv cov txheej txheem ntawm kev faib cell, DNA mus txog nws qhov siab tshaj plaws twist thiab yog sawv cev los ntawm mitotic chromosomes. Txhua strand tsim cov chromosome cais.
- Nyob rau hauv interphase, thaum cell DNA feem ntau decondensed, chromatin sib npaugqhov chaw ntawm lub nucleus los yog cov ntaub ntawv clumps pom nyob rau hauv ib lub teeb microscope. Xws li chromocenters feem ntau kuaj pom nyob ze ntawm daim nyias nyias.
Cov xeev no yog lwm txoj hauv kev, tag nrho cov chromosomes compacted tsis khaws cia nyob rau hauv lub interphase.
YEuchromatin thiab heterochromatin
Interphase chromatin yog ib chromosome uas tau poob nws cov duab compact. Lawv loops yog loosened, sau lub ntim ntawm nucleus. Muaj kev sib raug zoo ntawm qib ntawm decondensation thiab kev ua haujlwm ntawm chromatin.
Nws qhov chaw, tag nrho "unraveled", yog hu ua diffuse lossis nquag chromatin. Nws yog xyaum tsis pom nyob rau hauv lub teeb microscope tom qab staining. Qhov no yog vim DNA helix tsuas yog 2 nm tuab. Lwm lub npe yog euchromatin.
Lub xeev no muab cov enzymatic complexes nrog rau kev nkag mus rau semantic DNA tawg, lawv txuas dawb thiab ua haujlwm. Cov qauv ntawm tus tub txib RNA (kev hloov pauv) yog nyeem los ntawm thaj chaw sib txawv los ntawm RNA polymerases, lossis DNA nws tus kheej tau theej (replication). Qhov siab dua ntawm cov khoom siv hluavtaws ntawm lub sijhawm tam sim no, qhov ntau dua ntawm euchromatin hauv cov nucleus.
Diffuse seem ntawm chromatin alternate nrog compact, sib txawv twisted aav ntawm heterochromatin. Vim tias qhov ntom ntom ntau dua, stained heterochromatin pom meej meej hauv interphase nuclei.
Daim duab qhia chromatin ntawm qhov sib txawv ntawm kev sib cog lus:
- 1 - ob-stranded DNA molecule;
- 2 - histonecov proteins;
- 3 - DNA qhwv ib ncig ntawm histone complex rau 1.67 lem ua ib tug nucleosome;
- 4 - solenoid;
- 5 - interphase chromosome.
Subtleties of definition
Euchromatin ntawm lub sijhawm tshwj xeeb yuav tsis koom nrog cov txheej txheem hluavtaws. Nyob rau hauv cov ntaub ntawv no, nws yog ib ntus nyob rau hauv ib tug ntau compact lub xeev thiab yuav yuam kev rau heterochromatin.
Real heterochromatin, nws tseem hu ua constitutive, tsis nqa semantic load thiab decondenses nkaus xwb nyob rau hauv tus txheej txheem ntawm replication. Cov DNA ntawm cov chaw no muaj luv luv, rov ua ntu zus uas tsis yog code rau amino acids. Nyob rau hauv mitotic chromosomes, lawv yog nyob rau hauv cheeb tsam ntawm thawj constriction thiab telomeric endings. Lawv kuj tau cais cov ntu ntawm cov DNA uas tau sau tseg, tsim cov kab sib txuas (intercalary) fragments.
Yuav ua li cas euchromatin "ua haujlwm"
Euchromatin muaj cov noob uas thaum kawg txiav txim siab cov qauv ntawm cov proteins (cov noob qauv). Kev txiav txim siab ntawm nucleotide ib ntus rau hauv cov protein tshwm sim nrog kev pab ntawm tus neeg nruab nrab muaj peev xwm, tsis zoo li chromosomes, tawm hauv lub nucleus - tub txib RNA.
Thaum lub sijhawm sau ntawv, RNA yog tsim los ntawm DNA qauv los ntawm dawb adenyl, uridyl, cytidyl thiab guanyl nucleotides. Kev hloov pauv yog ua los ntawm enzyme complex RNA polymerase.
Qee cov noob txiav txim siab qhov sib lawv liag ntawm lwm hom RNA (kev thauj mus los thiab ribosomal) tsim nyog los ua kom tiav cov txheej txheem ntawm cov protein synthesis hauv cytoplasm los ntawmCov amino acids.
Heterochromatin ntawm ib qho chromosome feem ntau tau sib sau ua ke rau hauv chromocenter zoo cim. Nyob ib ncig ntawm nws yog loops ntawm despiralized euchromatin. Ua tsaug rau qhov kev teeb tsa ntawm cov tub ntxhais DNA, cov enzyme complexes thiab cov nucleotides dawb, tsim nyog rau kev siv cov haujlwm ntawm euchromatin, yooj yim haum rau cov ntsiab lus.
