Kev Npaj DNA lossis Kev Ntim Khoom Hauv Cov Cell
Nyob rau theem molecular, lub neej nyob hauv ntiaj teb yog tsim los ntawm lub hauv paus ntawm cov ntaub ntawv caj ces uas muaj nyob rau hauv DNA molecules. DNA, lossis deoxyribonucleic acid, yog ib qho polymer uas khaws cov lus qhia txog lub cev tseem ceeb rau kev loj hlob, kev ua haujlwm, kev loj hlob, thiab kev yug me nyuam ntawm txhua yam uas muaj sia. Txawm hais tias DNA tsuas yog muaj plaub hom nucleotides xwb - adenine (A), thymine (T), cytosine (C), thiab guanine (G) - lawv lub koom haum hauv cov cell yog qhov nyuaj heev. Cia peb tshawb nrhiav kom meej ntxiv txog li cas DNA tau teeb tsa, lossis ntim, hauv cov cell.
Cov Qauv Tseem Ceeb ntawm DNA
DNA muaj lub duab ob lub voj voog, uas James Watson thiab Francis Crick tau tshawb pom hauv xyoo 1953. Cov qauv no zoo li lub ntaiv uas ntswj, nrog cov khub hauv paus ua cov ntaiv thiab cov pob txha qab zib-phosphate ua cov tes tuav. Cov khub hauv paus ntawm adenine thiab thymine, thiab cytosine thiab guanine, txuas nrog los ntawm cov hydrogen bonds, muab kev ruaj khov rau ob lub voj voog.
Cov Histones thiab Nucleosomes
Hauv lub nucleus ntawm lub eukaryotic cell, ib lub DNA molecule tuaj yeem ntev ob peb meters thaum ncab tag. Kev sib txuas lub molecule loj no rau hauv lub nucleus uas ntsuas tsuas yog ob peb micrometers hauv txoj kab uas hla yuav tsum muaj lub tshuab ntim khoom zoo heev. Ib qho tseem ceeb ntawm kev ntim DNA yog cov protein hu ua histones.
Cov histones yog cov protein yooj yim uas muaj cov amino acids lysine thiab arginine ntau, ua rau lawv sib cuam tshuam tau zoo nrog cov DNA acidic. DNA raug qhwv ib ncig ntawm cov histones, tsim cov qauv hu ua nucleosomes. Txhua lub nucleosome muaj kwv yees li 147 khub DNA puag ncig ib pawg ntawm yim histones, tsim cov khoom ntim khoom yooj yim ntawm chromatin. Cov saw hlau ntawm nucleosomes no zoo li "txoj hlua ntawm cov hlaws dai" nyob rau hauv lub tshuab microscope.
Cov Chromatin thiab Chromosomes
Kev ntim DNA txuas ntxiv mus rau theem siab dua, qhov twg nucleosomes tau teeb tsa ua ib qho qauv me me thiab raug txiav txim siab hu ua chromatin. Muaj ob hom tseem ceeb ntawm chromatin: euchromatin thiab heterochromatin. Euchromatin yog daim ntawv qhib dua thiab ua haujlwm ntau dua, txhais tau tias DNA hauv cov cheeb tsam no nkag tau yooj yim dua rau cov tshuab sau ntawv. Qhov sib txawv, heterochromatin yog me me dua thiab feem ntau cuam tshuam nrog DNA tsis ua haujlwm.
Ntxiv mus, kev teeb tsa tsim cov chromosomes, cov qauv qib siab tshaj plaws ntawm DNA ntim, pom tau thaum lub sijhawm faib cell. Chromosomes yog daim ntawv me tshaj plaws ntawm DNA thiab ua kom muaj DNA replication meej yam tsis poob cov khoom tseem ceeb thaum lub sijhawm mitosis thiab meiosis. Tib neeg, piv txwv li, muaj 46 chromosomes hauv txhua lub cev cell.
Kev Cai Tswjfwm Ntim Khoom DNA
Kev ntim DNA tsis yog ib qho txheej txheem uas tsis hloov pauv; nws yog dynamic thiab cuam tshuam los ntawm ntau yam. Kev hloov kho Histone, xws li acetylation, methylation, phosphorylation, thiab ubiquitination, tuaj yeem hloov pauv kev sib cuam tshuam ntawm DNA thiab histones, yog li cuam tshuam rau chromatin density thiab DNA nkag mus rau kev sau ntawv. Piv txwv li, histone acetylation feem ntau yog txuam nrog euchromatin thiab active transcription, thaum methylation tuaj yeem ua lub luag haujlwm hauv kev tsim heterochromatin.
Ntxiv rau cov histones, kuj tseem muaj cov protein chromatin remodeling uas tuaj yeem txav mus los, txo qis, lossis rov tsim kho qhov chaw ntawm nucleosome, ntxiv kev hloov kho kev nkag mus rau cov noob caj noob ces. Tag nrho cov yam no ua haujlwm ua ke los ua kom zoo dua kev tswj hwm DNA kom tau raws li cov kev xav tau ntawm lub hlwb.
DNA Ntim Khoom Hauv Prokaryotes
Tsis zoo li eukaryotes, cov kab mob thiab lwm yam kab mob prokaryotic feem ntau muaj DNA puag ncig, es tsis yog linear, thiab tsis muaj lub nucleus uas khi nrog daim nyias nyias. Txawm hais tias yooj yim dua, DNA ntim hauv prokaryotes tsis tseem ceeb. Hauv cov kab mob, DNA raug compacted nrog kev pab los ntawm cov protein xws li HU thiab IHF, uas tswj cov supercoiling thiab tswj cov qauv nucleoid.
Qhov Tseem Ceeb ntawm DNA Ntim Khoom
Kev ntim DNA zoo tsis yog tsuas yog hais txog kev khaws cov ntaub ntawv caj ces xwb, tab sis kuj yog hais txog kev tswj hwm kev ua haujlwm ntawm cov noob caj ces. Qhov chaw thiab qhov ceev ntawm chromatin tuaj yeem cuam tshuam rau kev qhia tawm ntawm cov noob caj ces thiab, yog li ntawd, yog qhov tseem ceeb ntawm kev tshawb fawb ntau hauv epigenetics. Kev kawm txog cov qauv epigenetic tuaj yeem muab kev nkag siab txog ntau yam mob thiab kab mob, suav nrog mob qog noj ntshav thiab kev loj hlob tsis zoo.
Piv txwv li, kev hloov pauv ntawm cov qauv ntim DNA tuaj yeem ua rau muaj kev qhia tawm tsis zoo ntawm cov noob caj noob ces, uas cuam tshuam nrog kev loj hlob ntawm mob qog noj ntshav. Cov kev kho mob uas tsom mus rau kev hloov pauv histone lossis cov qauv chromatin qhia tau tias muaj peev xwm kho cov kab mob uas tshwm sim los ntawm kev tswj hwm epigenetic tsis zoo.
Xaus
Kev tswj lossis ntim cov DNA hauv cov cell yog ib qho txheej txheem nyuaj thiab ntxaws ntxaws uas ua lub luag haujlwm tseem ceeb hauv lub neej. Kev ntim DNA tsis yog tsuas yog cuam tshuam rau kev ruaj khov ntawm cov noob caj noob ces thaum lub sijhawm faib cell xwb tab sis kuj ua haujlwm ua tus tswj hwm, tswj hwm cov noob caj noob ces twg tau qhia tawm thaum lub sijhawm zoo thiab hauv qhov ntau thiab tsawg. Kev nkag siab txog cov ntsiab lus ntawm kev ntim DNA muab kev nkag siab tob txog cov hauv paus ntawm kev tshawb fawb txog cell thiab ua rau txoj hauv kev rau kev tsim cov kev kho mob tshiab rau cov kab mob caj ces thiab epigenetic. Raws li ib qho ntawm cov lus zais tshaj plaws hauv molecular biology, kev tshawb fawb hauv thaj chaw no yuav txuas ntxiv muab cov kev cov nyom thiab cov cib fim zoo rau cov kws tshawb fawb thoob ntiaj teb.
