Lub tswv yim ntawm "chromosome" tsis yog qhov tshiab hauv kev tshawb fawb raws li nws yuav zoo li thaum xub thawj siab ib muag. Thawj thawj zaug, lo lus no tau thov kom xaiv cov qauv intranuclear ntawm eukaryotic cell ntau tshaj 130 xyoo dhau los los ntawm morphologist W. Waldeyer. Embedded nyob rau hauv lub npe yog lub peev xwm ntawm lub intracellular qauv rau stain nrog yooj yim dyes.
Ua ntej ntawm tag nrho… Dab tsi yog chromatin?
Chromatin yog ib qho nucleoprotein complex. Namely, chromatin yog ib tug polymer uas muaj xws li tshwj xeeb chromosomal proteins, nucleosomes thiab DNA. Proteins tuaj yeem ua rau 65% ntawm qhov loj ntawm chromosome. Chromatin yog ib qho dynamic molecule thiab tuaj yeem siv ntau qhov kev teeb tsa.
Chromatin proteins ua ib feem tseem ceeb ntawm nws pawg thiab muab faib ua ob pawg:
- Histone proteins - muaj cov amino acids yooj yim hauv lawv cov muaj pes tsawg leeg (piv txwv li, arginine thiab lysine). Kev npaj ntawm histones yog chaotic nyob rau hauv daim ntawv ntawm blocks raws tag nrho ntev ntawm DNA molecule.
- Cov proteins uas tsis yog histone (kwv yees li 1/5 ntawm tag nrho cov histones) - yog cov protein ntauib tug matrix uas tsim ib tug structural network nyob rau hauv lub interphase nucleus. Nws yog nws uas yog lub hauv paus uas txiav txim siab lub morphology thiab metabolism ntawm lub nucleus.
Tam sim no, hauv cytogenetics, chromatin tau muab faib ua ob hom: heterochromatin thiab euchromatin. Kev faib cov chromatin rau hauv ob hom tshwm sim vim muaj peev xwm ntawm txhua hom kom stain nrog cov xim tshwj xeeb. Qhov no yog cov txheej txheem DNA zoo siv los ntawm cytologists.
YHeterochromatin
Heterochromatin yog ib feem ntawm chromosome ib nrab condensed hauv interphase. Functionally, heterochromatin tsis muaj nuj nqis, vim nws tsis ua haujlwm, tshwj xeeb hauv kev cuam tshuam nrog kev sau ntawv. Tab sis nws lub peev xwm los stain zoo yog siv dav hauv kev tshawb fawb histological.
qauv ntawm heterochromatin
Heterochromatin muaj cov qauv yooj yim (saib daim duab).
Heterochromatin tau ntim rau hauv globules hu ua nucleosomes. Nucleosomes tsim cov qauv ntau dua thiab yog li "kev cuam tshuam" nrog kev nyeem cov ntaub ntawv los ntawm DNA. Heterochromatin yog tsim nyob rau hauv cov txheej txheem ntawm methylation ntawm H3 histone ntawm lysine 9, thiab tom qab ntawd cuam tshuam nrog cov protein 1 (HP1 - Heterochromatin Protein 1). Kuj cuam tshuam nrog lwm cov proteins, suav nrog H3K9-methyltransferases. Xws li cov protein ntau ntawm kev sib cuam tshuam nrog ib leeg yog ib qho mob rau kev tswj hwm heterochromatin thiab nws qhov kev faib tawm. Cov qauv tseem ceeb ntawm DNA tsis cuam tshuam rau kev tsim ntawm heterochromatin.
Heterochromatin tsis yog tsuas yog cais qhov chaw xwb, tab sis kuj tseem muaj cov chromosomes tag nrho, uas tseem nyob hauv lub xeev condensed thoob plaws hauv lub voj voog ntawm tes. Lawv nyob rau hauv S-theem thiab raug replication. Cov kws tshawb fawb ntseeg tias thaj chaw heterochromatin tsis nqa cov noob uas encode cov protein, lossis cov noob no tsawg heev. Hloov chaw ntawm cov noob no, cov nucleotide sequences ntawm heterochromatin feem ntau muaj qhov yooj yim rov ua dua.
Type of heterochromatin
Heterochromatin yog ob hom: facultative thiab structural.
- Facultative heterochromatin yog chromatin uas yog tsim thaum lub sij hawm tsim ib lub helix ntawm ib qho ntawm ob chromosomes ntawm tib hom, nws tsis yog ib txwm heterochromatic, tab sis lub sij hawm. Nws muaj cov noob nrog cov ntaub ntawv keeb kwm yav dhau los. Nws yog nyeem thaum nws nkag mus rau hauv lub xeev euchromatic. Lub xeev condensed rau facultative heterochromatin yog ib ntus tshwm sim. Qhov no yog nws qhov sib txawv tseem ceeb ntawm cov qauv tsim. Ib qho piv txwv ntawm facultative heterochromatin yog lub cev ntawm chromatin, uas txiav txim siab poj niam txiv neej. Txij li cov qauv no muaj ob homologous X-chromosomes ntawm somatic hlwb, ib qho ntawm lawv tuaj yeem tsim facultative heterochromatin.
- Structural heterochromatin yog cov qauv tsim los ntawm lub xeev coiled heev. Nws txuas ntxiv mus thoob plaws lub voj voog. Raws li tau hais los saum toj no, lub xeev condensed rau cov qauv heterochromatin yog qhov tshwm sim tas li, sib piv rau ib qho kev xaiv. Cov qauv heterochromatin kuj hu uaconstitutive, nws pom zoo los ntawm C-xim. Nws nyob deb ntawm lub nucleus thiab nyob hauv cheeb tsam centromeric, tab sis qee zaum nws nyob hauv lwm thaj tsam ntawm chromosome. Feem ntau, thaum interphase, sib sau ua ke ntawm ntau ntu ntawm cov qauv heterochromatin tuaj yeem tshwm sim, uas ua rau tsim cov chromocenters. Hauv hom heterochromatin no, tsis muaj cov cuab yeej hloov pauv, uas yog, tsis muaj cov txheej txheem cov noob. Lub luag haujlwm ntawm ib ntu ntawm chromosome tsis meej meej txog tam sim no, yog li cov kws tshawb fawb tsuas yog txhawb nqa txoj haujlwm xwb.
Euchromatin
Euchromatin yog ib feem ntawm chromosomes uas yog decondensed hauv interphase. Xws li ib qho chaw yog xoob, tab sis tib lub sijhawm me me compact qauv.
Cov yam ntxwv ntawm euchromatin
hom chromatin no ua haujlwm thiab ua haujlwm zoo. Nws tsis muaj cov cuab yeej ntawm staining thiab tsis txiav txim siab los ntawm kev tshawb fawb histological. Nyob rau theem ntawm mitosis, yuav luag tag nrho cov euchromatin condenses thiab dhau los ua ib feem ntawm cov chromosome. Synthetic functions nyob rau lub sij hawm no, cov chromosomes tsis ua. Yog li ntawd, cellular chromosomes tuaj yeem nyob rau hauv ob lub luag haujlwm thiab cov qauv:
- Ua haujlwm lossis ua haujlwm hauv xeev. Lub sijhawm no, cov chromosomes yuav luag tag lossis tag nrho decondensed. Lawv koom nrog hauv cov txheej txheem ntawm transcription thiab reduplication. Tag nrho cov txheej txheem no tshwm sim ncaj qha hauv lub cell nucleus.
- Lub xeev tsis ua haujlwm ntawm metabolic dormancy (tsis ua haujlwm). Hauv lub xeev no, cov chromosomesyog condensed mus rau qhov siab tshaj plaws thiab ua ib qho kev thauj mus los ntawm cov khoom siv caj ces mus rau cov menyuam ntxhais. Hauv lub xeev no, cov khoom siv caj ces kuj raug faib.
Nyob rau theem kawg ntawm mitosis, despiralization tshwm sim thiab cov xim tsis muaj zog nyob rau hauv daim ntawv ntawm cov xov uas muaj cov noob caj noob ces raug tsim.
Cov qauv ntawm txhua tus chromosome muaj nws tus kheej, tshwj xeeb, txawv ntawm qhov chaw ntawm chromatin: euchromatin thiab heterochromatin. Cov yam ntxwv ntawm cov hlwb no tso cai rau cytogeneticists txheeb xyuas tus kheej chromosomes.
