Kev teeb tsa genome hauv eukaryotic hlwb
Cov genomes ntawm eukaryotic cells—xws li cov tsiaj, nroj tsuag, fungi, thiab protists—muaj ib theem nyuaj thiab muaj kev teeb tsa zoo heev. Tsis zoo li prokaryotes, uas feem ntau muaj DNA puag ncig nyob hauv ib cheeb tsam (lub nucleoid), eukaryotic cells khaws cia feem ntau ntawm lawv cov khoom siv caj ces hauv lub nucleus hauv daim ntawv ntawm linear chromosomes. Txhawm rau kom haum rau DNA ntev hauv lub nucleus me me thaum tseem yooj yim nkag mus rau kev qhia tawm thiab kev rov ua dua, eukaryotic cells tau tsim ib qho kev ntim khoom DNA zoo thiab dynamic. Lub koom haum genome no tsis yog tsuas yog ib qho teeb meem ntawm "kev khaws cia," tab sis kuj ntawm "kev tswj hwm" thaum twg thiab qhov twg cov noob ua haujlwm.
1. Cov Cheebtsam Tseem Ceeb ntawm Eukaryotic Genome
Cov eukaryotic genome yog tsim los ntawm DNA uas muab faib ua ntau lub chromosomes. Tus naj npawb ntawm cov chromosomes sib txawv ntawm cov tsiaj; tib neeg muaj 46 chromosomes (23 khub), mov muaj 24, thiab qee cov nroj tsuag tuaj yeem muaj ntau pua. Ntxiv rau lub nuclear genome, eukaryotes kuj muaj DNA hauv organelles xws li mitochondria (hauv yuav luag txhua eukaryotes) thiab chloroplasts (hauv cov nroj tsuag thiab algae). Cov DNA hauv cov organelles no feem ntau me dua thiab nqa cov noob tseem ceeb ntsig txog kev ua pa ntawm tes lossis photosynthesis.
Hauv cov noob caj noob ces ntawm lub nucleus, muaj cov noob caj noob ces uas sau cov protein, cov noob caj noob ces uas sau cov RNA (piv txwv li, rRNA, tRNA, miRNA), thiab cov cheeb tsam uas tsis sau cov protein, feem ntau muaj ntau dua li cov cheeb tsam uas sau cov protein tiag tiag. Cov cheeb tsam uas tsis sau cov protein tsis tas yuav yog "tsis muaj txiaj ntsig"; ntau ntawm lawv ua haujlwm ua cov khoom tswj hwm xws li cov neeg txhawb nqa, cov neeg txhawb nqa, cov neeg ua kom ntsiag to, thiab cov neeg rwb thaiv tsev uas tswj hwm thaum cov noob caj noob ces ua haujlwm.
2. Kev Ntim DNA: Los ntawm Double Helix DNA mus rau Chromosomes
Qhov ntev ntawm eukaryotic DNA yog qhov txawv heev: yog tias DNA hauv ib lub cell tib neeg raug ncab tawm, nws yuav ntev li ob meters, txawm tias lub nucleus ntawm lub cell tsuas yog ob peb micrometers hauv txoj kab uas hla. Qhov kev sib tw no tau kov yeej los ntawm kev ntim ntau txheej siv cov protein histone thiab lwm cov protein qauv.
a. Nucleosome: Chav Tseem Ceeb ntawm Chromatin
Qib yooj yim tshaj plaws ntawm kev ntim khoom yog lub nucleosome, uas yog DNA qhwv ib puag ncig ntawm yim cov protein histone (histone octamer). Kwv yees li 147 khub DNA puag ncig cov histones, tsim cov qauv "beads-on-a-string". Nruab nrab ntawm cov nucleosomes yog cov txuas DNA strands ntawm ntau qhov ntev, feem ntau ruaj khov los ntawm histone H1.
b. Cov Chromatin Fibers thiab Cov Qib Ntim Khoom Siab Tshaj Plaws
Cov nucleosomes tsis nres ntawm cov qauv "beaded"; lawv tuaj yeem sib cuam tshuam thiab tsim cov fibers denser. Classically, cov no feem ntau hu ua 30-nm fibers, txawm hais tias cov ntsiab lus ntawm cov qauv no hauv cov cell muaj sia nyob yog dynamic ntau dua thiab tsis yog ib txwm sib xws. Ntxiv mus, chromatin fibers tsim cov voj voog anchored rau lub nuclear protein framework, yog li teeb tsa DNA spatially.
c. Cov Chromosomes Metaphase
Thaum lub sij hawm faib cov cell (mitosis thiab meiosis), chromatin sib sau ua ke kom sib txuas ua ke ua cov metaphase chromosomes, uas pom tau yooj yim hauv qab lub tshuab microscope. Qhov kev sib sau ua ke no yog qhov tseem ceeb rau kev cais DNA ua cov cell ntxhais kom raug yam tsis muaj kev sib txuas lossis tawg.
3. Chromatin: Euchromatin thiab Heterochromatin
Kev teeb tsa genome kuj tseem cuam tshuam txog DNA "qhib" lossis "kaw" rau kev nkag mus los ntawm cov tshuab sau ntawv.
– Euchromatin yog ib hom chromatin uas xoob dua, muaj ntau cov noob caj noob ces uas nquag ua haujlwm, thiab yooj yim dua rau kev sau ntawv. Thaj chaw no feem ntau "qhib dua," uas tso cai rau cov yam ntxwv sau ntawv thiab RNA polymerase khi rau DNA.
– Heterochromatin yog ib hom chromatin uas me dua, feem ntau muaj kev ua haujlwm transcription tsawg. Heterochromatin tuaj yeem yog constitutive (ib txwm me me, piv txwv li, ntawm centromeres thiab telomeres) lossis facultative (tuaj yeem sib txawv nyob ntawm hom cell lossis theem kev loj hlob, piv txwv li, X chromosome uas tsis ua haujlwm hauv cov tsiaj txhu poj niam).
Qhov sib txawv no qhia tau hais tias DNA ntim tsis yog tsuas yog lub cev xwb, tab sis kuj yog ib txoj hauv kev rau kev tswj hwm cov noob caj noob ces.
4. Cov Qauv ntawm Chromosomes: Centromeres, Telomeres, thiab Keeb Kwm ntawm Kev Rov Ua Dua
Txhua lub chromosome eukaryotic muaj cov khoom tseem ceeb uas ua kom muaj kev ruaj khov thiab kev txais qub txeeg qub teg:
- Lub centromere yog thaj chaw uas kinetochore, ib qho protein uas txuas cov chromosomes rau cov spindle fibers thaum lub sijhawm faib cell, tsim. Lub centromere yog qhov tseem ceeb rau kev sib cais ntawm cov viv ncaus chromatids.
- Telomeres yog qhov kawg ntawm cov chromosomes, uas muaj cov DNA rov ua dua thiab cov protein tiv thaiv. Telomeres tiv thaiv cov chromosomes kawg kom tsis txhob raug pom tias yog DNA puas lawm thiab tiv thaiv kev sib xyaw ntawm cov chromosomes. Telomere luv luv tshwm sim thaum lub sijhawm DNA replication, thiab cov enzyme telomerase tuaj yeem ua rau lawv ntev dua hauv qee lub hlwb.
- Lub hauv paus chiv keeb ntawm kev rov ua dua (ori) yog qhov pib ntawm DNA rov ua dua. Hauv eukaryotes, muaj ntau oris ntawm ib qho chromosome, uas ua rau kev rov ua dua tshwm sim sai dua thiab ua tau zoo dua.
5. 3D Architecture ntawm Genome hauv Nucleus
Kev tshawb fawb niaj hnub no qhia tau hais tias cov noob caj noob ces tsis tau raug teeb tsa yam tsis muaj kev npaj ua ntej hauv lub nucleus ntawm lub cell. DNA tau muab tso rau hauv qhov chaw peb-seem, uas cuam tshuam rau kev qhia tawm ntawm cov noob caj noob ces.
a. Thaj Chaw Chromosome
Txhua lub chromosome feem ntau nyob hauv ib cheeb tsam tshwj xeeb hauv lub nucleus hu ua thaj chaw chromosome. Txawm hais tias muaj kev sib cuam tshuam ntawm cov chromosomes, kev sib cais thaj chaw pab tswj kev txiav txim thiab txo qhov sib xyaw.
b. Kev Sib Txuas Lus thiab Kev Sib Txuas Lus Nyob Deb
Cov noob caj noob ces tuaj yeem ua haujlwm los ntawm cov khoom txhawb nqa uas nyob deb ntawm kab tab sis nyob ze ntawm qhov chaw los ntawm kev tsim cov voj voog chromatin. Cov protein xws li CTCF thiab cov cohesin complex ua lub luag haujlwm tseem ceeb hauv kev tsim thiab tswj cov voj voog no.
c. TAD (Cov Cheeb Tsam Sib Txuas Nrog Topologically)
Cov genome kuj tseem muab faib ua cov cheeb tsam sib cuam tshuam hu ua TADs, cov cheeb tsam ntawm DNA uas sib cuam tshuam nrog lawv tus kheej ntau dua li lwm cov cheeb tsam. TADs pab ua kom ntseeg tau tias cov enhancers ua kom cov noob "yog" ua haujlwm thiab tiv thaiv cov tsis xav tau kom tsis txhob ua haujlwm.
6. Epigenetics: Tswj Cov Genes Yam Tsis Hloov Cov DNA Sequence
Kev teeb tsa ntawm cov eukaryotic genomes yog cuam tshuam los ntawm cov txheej txheem epigenetic, uas yog kev hloov pauv uas cuam tshuam rau kev qhia tawm ntawm cov noob caj noob ces yam tsis hloov pauv cov kab ke DNA. Ob lub txheej txheem tseem ceeb yog:
- Kev hloov kho Histone, xws li acetylation, methylation, phosphorylation, thiab ubiquitination. Histone acetylation feem ntau ua rau chromatin qhib dua thiab ua rau kev sau ntawv ntau ntxiv, thaum qee hom methylation tuaj yeem ua kom muaj zog lossis tswj kev sau ntawv nyob ntawm qhov chaw ntawm cov seem.
- DNA methylation, uas feem ntau tshwm sim ntawm cytosines hauv CpG cov ntsiab lus hauv cov tsiaj. DNA methylation feem ntau cuam tshuam nrog kev tshem tawm transcriptional thiab heterochromatin tsim.
Epigenetics tso cai rau tib lub genome los tsim cov cell sib txawv nrog cov haujlwm sib txawv, xws li cov hlab ntsha, cov leeg nqaij, thiab cov qe ntshav, los ntawm cov qauv sib txawv ntawm kev qhia tawm gene.
7. Cov Genomes Organelle: Mitochondria thiab Chloroplasts
Ntxiv rau lub genome nuclear, eukaryotes muaj mitochondrial genomes, thiab hauv cov nroj tsuag, chloroplasts. Organellar genomes feem ntau yog voj voog thiab niam tau txais los ntawm ntau hom tsiaj. Txawm hais tias tus lej ntawm cov noob caj noob ces hauv mitochondria yog me me, lawv txoj haujlwm tseem ceeb rau kev tsim hluav taws xob. Qhov nthuav yog, ntau cov noob caj noob ces yav dhau los pom hauv cov organelles no tau tsiv mus rau lub nucleus thaum lub sijhawm evolution, yog li organelle ua haujlwm feem ntau nyob ntawm cov protein encoded los ntawm lub nuclear genome.
8. Kev cuam tshuam ntawm Genome Organization rau Kev Noj Qab Haus Huv thiab Kev Hloov Pauv
Kev teeb tsa genome kom zoo ua kom muaj kev ruaj khov ntawm cov noob caj noob ces. Kev puas tsuaj ntawm Telomere, qhov yuam kev hauv kev tsim chromatin, lossis kev cuam tshuam ntawm kev tswj hwm epigenetic tuaj yeem ua rau muaj ntau yam kab mob, suav nrog mob qog noj ntshav thiab kev loj hlob tsis zoo. Piv txwv li, kev hloov pauv hauv cov qauv DNA methylation tuaj yeem ua rau cov oncogenes ua haujlwm lossis ua rau cov noob caj noob ces tsis ua haujlwm. Ntxiv mus, kev hloov pauv hauv cov qauv chromosome, xws li kev hloov pauv, tuaj yeem ua ke ob lub noob, ua rau cov protein sib xyaw ua ke tsis zoo.
Hauv kev hloov zuj zus, kev teeb tsa genome tso cai rau kev hloov pauv: kev luam tawm gene, kev sib koom ua ke, thiab kev hloov pauv hauv cov ntsiab lus tswj hwm tuaj yeem tsim cov haujlwm tshiab yam tsis hloov pauv tag nrho lub cev. Yog li, qhov nyuaj ntawm eukaryotic feem ntau tshwm sim los ntawm lub peev xwm los tswj kev qhia gene kom meej los ntawm kev teeb tsa genome ntau txheej.
Xaus
Lub koom haum genome hauv eukaryotic hlwb yog ib lub cev muaj zog thiab muaj zog heev, xws li nucleosomes ua lub hauv paus tseem ceeb, los ntawm kev tsim euchromatin thiab heterochromatin, mus rau peb-seem architectures xws li chromosome territories thiab TADs. Tag nrho cov theem ntawm kev koom ua ke no ua lub luag haujlwm tseem ceeb hauv kev ua kom ntseeg tau tias DNA raug compacted, tiv thaiv, replicate, inherited, thiab qhia raws li lub cell xav tau. Los ntawm epigenetic mechanisms thiab spatial regulation hauv nucleus, eukaryotic hlwb muaj peev xwm tswj tau ntau pua mus rau ntau txhiab tus noob. Kev nkag siab txog kev koom ua ke genome tsis yog tsuas yog qhov tseem ceeb rau kev tshawb fawb tseem ceeb xwb tab sis kuj tseem ceeb rau kev nkag siab txog kab mob, kev laus, thiab kev tsim kho tshiab biotechnological yav tom ntej.
