Tsis zoo li eukaryotes, cov kab mob tsis muaj cov nucleus tsim, tab sis lawv cov DNA tsis tawg thoob plaws hauv lub xov tooj ntawm tes, tab sis yog concentrated nyob rau hauv cov qauv compact hu ua nucleoid. Hauv cov ntsiab lus ua haujlwm, nws yog qhov ua haujlwm zoo ntawm lub tshuab hluav taws xob nuclear.
Nucleoid yog dab tsi
Ib kab mob nucleoid yog thaj chaw hauv lawv cov hlwb uas muaj cov khoom siv caj ces. Tsis zoo li eukaryotic nucleus, nws tsis yog sib cais los ntawm ib daim nyias nyias los ntawm qhov seem ntawm cov cellular cov ntsiab lus thiab tsis muaj cov duab mus tas li. Txawm li cas los xij, cov cuab yeej caj ces ntawm cov kab mob yog cais tawm ntawm cytoplasm.
Lo lus nws tus kheej txhais tau tias "zoo li nucleus" lossis "nuclear region". Cov qauv no tau pom thawj zaug hauv xyoo 1890 los ntawm zoologist Otto Buchli, tab sis nws qhov sib txawv ntawm cov khoom siv caj ces ntawm eukaryotes tau txheeb pom nyob rau thaum ntxov 1950s ua tsaug rau electron microscopy technology. Lub npe "nucleoid" sib raug rau lub tswvyim ntawm "cov kab mob chromosome", yog tias tom kawg muaj nyob rau hauv ib lub xovtooj ntawm ib daim qauv.
Nucleoid tsis suav nrog plasmids uasyog cov ntsiab lus extrachromosomal ntawm cov kab mob genome.
Ntawm cov kab mob nucleoid
Feem ntau, cov nucleoid nyob hauv nruab nrab ntawm cov kab mob ntawm tes thiab yog taw qhia raws nws axis. Qhov ntim ntawm qhov kev cog lus no tsis pub tshaj 0.5 microns3, thiab qhov hnyav molecular txawv ntawm 1 × 10 9 rau 3 × 109 d alton. Ntawm qee cov ntsiab lus, cov nucleoid yog khi rau ntawm lub cell membrane.
Cov kab mob nucleoid muaj peb yam:
- DNA.
- Cov txheej txheem thiab kev tswj hwm cov protein.
- RNA.
DNA muaj lub koom haum chromosomal uas txawv ntawm eukaryotic. Feem ntau, cov kab mob nucleoid muaj ib chromosome lossis ob peb daim ntawv luam ntawm nws (nrog rau kev loj hlob, lawv cov lej nce mus txog 8 lossis ntau dua). Qhov ntsuas no txawv nyob ntawm hom thiab theem ntawm lub neej voj voog ntawm cov kab mob. Qee cov kab mob muaj ntau yam chromosomes nrog ntau pawg ntawm cov noob.
Nyob rau hauv nruab nrab ntawm nucleoid DNA yog ntim nruj heev. Cov cheeb tsam no tsis tuaj yeem nkag mus rau ribosomes, replication thiab transcription enzymes. Ntawm qhov tsis sib xws, deoxyribonucleic loops ntawm thaj tsam peripheral ntawm nucleoid yog nyob rau hauv kev sib cuag ncaj qha nrog cytoplasm thiab sawv cev rau thaj chaw nquag ntawm cov kab mob genome.
Tus nqi ntawm cov protein nyob hauv cov kab mob nucleoid tsis tshaj 10%, uas yog kwv yees li 5 npaug tsawg dua hauv eukaryotic chromatin. Feem ntau cov proteins yog txuam nrog DNA thiab koom nrog nws cov qauv. RNA yog ib yam khoomtranscription ntawm kab mob genes, uas yog nqa tawm nyob rau hauv periphery ntawm lub nucleoid.
Cov kab mob caj ces ntawm cov kab mob yog ib qho kev tsim muaj peev xwm hloov tau nws cov duab thiab cov qauv tsim. Nws tsis muaj cov nucleoli thiab mitotic apparatus yam ntxwv ntawm lub nucleus ntawm eukaryotic cell.
Bacterial chromosome
Feem ntau, cov kab mob nucleoid chromosomes muaj lub nplhaib kaw. Linear chromosomes muaj tsawg dua. Txawm li cas los xij, cov qauv no muaj tib lub DNA molecule, uas muaj cov noob caj noob ces tsim nyog rau kev ciaj sia ntawm cov kab mob.
Chromosomal DNA tau ua tiav hauv daim ntawv ntawm supercoiled loops. Tus naj npawb ntawm loops ib chromosome txawv ntawm 12 mus rau 80. Txhua chromosome yog ib tug tag nrho-fledged replicon, txij li thaum muab ob npaug rau DNA yog theej tag nrho. Cov txheej txheem no ib txwm pib los ntawm keeb kwm ntawm kev rov ua dua tshiab (OriC), uas txuas nrog rau plasma membrane.
Tag nrho ntev ntawm DNA molecule hauv chromosome yog ntau qhov kev txiav txim siab ntau dua li qhov loj ntawm cov kab mob, yog li nws yuav tsum tau ntim nws, tab sis thaum tswj kev ua haujlwm.
Hauv eukaryotic chromatin, cov haujlwm no yog ua los ntawm cov proteins tseem ceeb - histones. Cov kab mob nucleoid muaj DNA-binding proteins uas yog lub luag haujlwm rau lub koom haum ntawm cov khoom siv caj ces, thiab tseem cuam tshuam rau cov noob caj noob ces thiab DNA replication.
Nucleoid-associated proteins suav nrog:
- histone-zoo li proteins HU, H-NS, FIS thiab IHF;
- topoisomerases;
- proteins ntawm SMC tsev neeg.
2 pab pawg kawg muaj qhov cuam tshuam loj tshaj plaws ntawm cov khoom siv caj ces.
Neutralization ntawm qhov tsis zoo nqi ntawm chromosomal DNA yog ua los ntawm polyamines thiab magnesium ions.
Lub luag haujlwm lom neeg ntawm nucleoid
Ua ntej tshaj, cov nucleoid yog qhov tsim nyog rau cov kab mob txhawm rau khaws thiab xa cov ntaub ntawv keeb kwm yav dhau los, nrog rau kev siv nws ntawm qib cellular synthesis. Hauv lwm lo lus, lub luag haujlwm lom neeg ntawm qhov tsim no yog tib yam li DNA.
Lwm cov kab mob nucleoid muaj xws li:
- localization thiab compaction ntawm genetic khoom;
- functional DNA ntim;
- kev tswj cov metabolism.
Y
DNA structuring tsis tsuas yog tso cai rau lub molecule kom haum nyob rau hauv ib tug microscopic cell, tab sis kuj tsim tej yam kev mob rau lub qub ntws ntawm replication thiab transcription txheej txheem.
Cov yam ntxwv ntawm lub koom haum molecular ntawm nucleoid tsim cov xwm txheej rau kev tswj cov cellular metabolism los ntawm kev hloov pauv DNA conformation. Kev tswj hwm tshwm sim los ntawm kev xa tawm qee ntu ntawm chromosome rau hauv cytoplasm, uas ua rau lawv muaj rau cov enzymes transcription, los yog rov qab, los ntawm rub lawv hauv.
Kev Tshawb Fawb
Muaj 3 txoj hauv kev kom pom qhov pom ntawm nucleoid hauv cov kab mob:
- lub teeb microscopy;
- phase contrast microscopy;
- electron microscopy.
Nyob ntawm txoj kevkev npaj ntawm kev npaj thiab kev tshawb fawb txoj kev, lub nucleoid tej zaum yuav txawv.
Lub teeb microscopy
txhawm rau kuaj pom lub nucleoid siv lub teeb pom kev zoo, cov kab mob ua ntej stained kom cov nucleoid muaj xim txawv ntawm cov ntsiab lus ntawm tes, txwv tsis pub cov qauv no yuav tsis pom. Nws tseem yuav tsum tau kho cov kab mob ntawm lub iav swb (qhov no, cov kab mob tuag).
Los ntawm lub lens ntawm lub teeb pom kev zoo, lub nucleoid zoo li cov taum zoo li tsim nrog thaj tsam ntshiab, uas nyob hauv nruab nrab ntawm lub xovtooj.
Txoj Kev Xim
Feem ntau, cov kab mob staining hauv qab no yog siv los pom cov nucleoid los ntawm lub teeb microscopy:
- raws li Romanovsky-Giemsa;
- Felgen method.
Thaum staining raws li Romanovsky-Giemsa, cov kab mob tau kho ua ntej ntawm lub khob swb nrog methyl cawv, thiab tom qab ntawd rau 10-20 feeb lawv tau muab tshuaj txhuam nrog cov xim los ntawm kev sib npaug ntawm azure, eonine thiab methylene xiav., yaj hauv methanol. Yog li ntawd, cov nucleoid ua ntshav thiab cytoplasm ua liab liab. Ua ntej microscopy, cov stain yog drained thiab cov swb yog ntxuav nrog distillate thiab qhuav.
Txoj kev Feulgen siv tsis muaj zog acid hydrolysis. Yog li ntawd, cov deoxyribose tso tawm mus rau hauv daim ntawv aldehyde thiab cuam tshuam nrog fuchsine-sulphurous acid ntawm Schiff reagent. Yog li ntawd, cov nucleoid ua liab, thiab cytoplasm ua xiav.
Phase contrast microscopy
Phase contrast microscopy muajkev daws teeb meem siab dua li lub teeb. Txoj kev no tsis tas yuav kho thiab staining ntawm kev npaj - kev soj ntsuam yuav siv qhov chaw rau cov kab mob nyob. Lub nucleoid nyob rau hauv cov hlwb zoo li lub teeb oval cheeb tsam tiv thaiv keeb kwm yav dhau ntawm tsaus cytoplasm. Ib txoj hauv kev zoo dua tuaj yeem ua los ntawm kev siv tshuaj fluorescent.
Nucleoid nrhiav pom nrog lub tshuab ntsuas hluav taws xob
Muaj 2 txoj hauv kev los npaj kev npaj rau kev kuaj nucleoid nyob rau hauv lub tshuab ntsuas hluav taws xob:
- ultra-thin cut;
- Txiav cov kab mob khov.
Nyob rau hauv electron micrographs ntawm ib qho ultrathin seem ntawm cov kab mob, cov nucleoid muaj qhov pom ntawm cov qauv network ntom ntom uas muaj cov ntaub nyias nyias, uas zoo li sib zog dua li ntawm ib puag ncig cytoplasm.
Ntawm ib ntu ntawm cov kab mob khov tom qab tiv thaiv kab mob, cov nucleoid zoo li cov qauv zoo li coral nrog cov tub ntxhais ntom ntom thiab nyias nyias nkag mus rau hauv cytoplasm.
Hauv cov duab hluav taws xob, cov kab mob nucleoid feem ntau nyob hauv nruab nrab ntawm lub xovtooj ntawm tes thiab muaj qhov ntim me dua li ntawm lub cell nyob. Qhov no yog vim raug cov tshuaj siv los kho qhov kev npaj.
