Deoxyribonucleic acid - DNA - ua haujlwm raws li cov ntaub ntawv keeb kwm xa mus los ntawm cov kab mob muaj sia mus rau lwm tiam neeg, thiab cov matrix rau kev tsim cov proteins thiab ntau yam kev tswj hwm uas xav tau los ntawm lub cev hauv cov txheej txheem ntawm kev loj hlob thiab lub neej. Hauv tsab xov xwm no, peb yuav tsom mus rau dab tsi yog cov qauv zoo tshaj plaws ntawm DNA qauv. Peb tseem yuav ua tib zoo saib seb cov ntaub ntawv no tau ua li cas thiab nyob rau hauv daim ntawv DNA nyob hauv lub cell li cas.
Qib ntawm lub koom haum ntawm DNA molecule
Muaj plaub theem uas txiav txim siab tus qauv thiab morphology ntawm no loj molecule:
- theem pib, lossis qauv, yog qhov kev txiav txim ntawm nucleotides hauv cov saw.
- Tus qauv thib ob yog lub npe nrov "ob chav helix". Nws yog cov kab lus no uas tau txiav txim siab, txawm hais tias qhov tseeb xws li cov qauv zoo ib yam li cov ntsia hlau.
- Cov qauv tertiary yog tsim los ntawm qhov tseeb tias tsis muaj zog hydrogen bonds tshwm sim ntawm tus kheej ntu ntawm ob-stranded twisted strand ntawm DNA,muab lub molecule ib tug complex spatial conformation.
- Cov qauv quaternary twb yog ib qho nyuaj ntawm DNA nrog qee cov proteins thiab RNA. Hauv qhov kev teeb tsa no, DNA tau ntim rau hauv chromosomes hauv cell nucleus.
Primary Structure: Cheebtsam ntawm DNA
Cov blocks uas cov macromolecule ntawm deoxyribonucleic acid tsim yog nucleotides, uas yog cov tebchaw, txhua qhov suav nrog:
- nitrogenous puag - adenine, guanine, thymine lossis cytosine. Adenine thiab guanine belongs rau pawg purine hauv paus, cytosine thiab thymine belongs rau pyrimidine;
- tsib-carbon monosaccharide deoxyribose;
- Orthophosphoric acid residue.
Hauv kev tsim cov saw hlau polynucleotide, lub luag haujlwm tseem ceeb yog ua los ntawm kev txiav txim ntawm cov pab pawg tsim los ntawm carbon atoms nyob rau hauv ib puag ncig qab zib molecule. Cov phosphate residue hauv nucleotide txuas nrog 5'-pab pawg (nyeem "tsib primes") ntawm deoxyribose, uas yog, mus rau tsib carbon atom. Cov saw txuas ntxiv tshwm sim los ntawm kev txuas cov phosphate residue ntawm cov nucleotide tom ntej mus rau dawb 3'-pab pawg ntawm deoxyribose.
Yog li, thawj cov qauv ntawm DNA nyob rau hauv daim ntawv ntawm ib tug polynucleotide saw muaj 3'- thiab 5'-kawg. Cov cuab yeej ntawm DNA molecule no hu ua polarity: kev sib txuas ntawm cov saw hlau tsuas tuaj yeem mus rau hauv ib qho kev taw qhia.
Kev tsim kho theem nrab
kauj ruam tom ntej hauv lub koom haum txheej txheem ntawm DNA yog raws li lub hauv paus ntsiab lus ntawm complementarity ntawm nitrogenous bases - lawv muaj peev xwm sib txuas ua ke nrog ib leeg.los ntawm hydrogen bonds. Complementarity - kev sib txuas lus - tshwm sim vim adenine thiab thymine tsim ib daim ntawv cog lus ob, thiab guanine thiab cytosine tsim ib daim ntawv cog lus triple. Yog li ntawd, thaum tsim ob txoj saw, cov hauv paus no sawv ntsug ntawm ib leeg, tsim cov khub sib xws.
Polynucleotide sequences nyob rau hauv cov qauv thib ob antiparallel. Yog li, yog tias ib qho ntawm cov saw hlau zoo li 3' - AGGZATAA - 5', ces qhov ntxeev yuav zoo li no: 3' - TTATGTST - 5'.
Thaum ib lub DNA molecule tsim, ob npaug polynucleotide saw yog twisted, thiab cov concentration ntawm ntsev, dej saturation, thiab cov qauv ntawm lub macromolecule nws tus kheej txiav txim seb dab tsi cov ntaub ntawv DNA yuav coj mus rau hauv ib tug muab kev cai kauj ruam. Ob peb daim ntawv no paub, txhais los ntawm Latin ntawv A, B, C, D, E, Z.
Kev teeb tsa C, D thiab E tsis pom nyob rau hauv cov tsiaj qus thiab tsuas yog tau pom nyob rau hauv lub chaw kuaj mob xwb. Peb yuav saib cov ntaub ntawv tseem ceeb ntawm DNA: lub npe hu ua canonical A thiab B, nrog rau Z configuration.
A-DNA yog cov molecule qhuav
A-zoo yog ib sab tes ntsia hlau nrog 11 lub hauv paus ua ke hauv txhua qhov tig. Nws txoj kab uas hla yog 2.3 nm, thiab qhov ntev ntawm ib tig ntawm kauv yog 2.5 nm. Cov dav hlau tsim los ntawm lub hauv paus ua ke muaj txoj kab nqes ntawm 20 ° nrog kev hwm rau lub axis ntawm cov molecule. Cov nucleotides nyob ib puag ncig yog compactly teem nyob rau hauv chains - tsuas muaj 0.23 nm ntawm lawv.
Daim ntawv DNA no tshwm sim nrog dej tsis tshua muaj dej thiab nrog kev nce ionic concentration ntawm sodium thiab potassium. Nws yog ib yam raucov txheej txheem uas DNA tsim ib qho nyuaj nrog RNA, txij li thaum kawg tsis tuaj yeem coj lwm yam ntaub ntawv. Tsis tas li ntawd, A-daim ntawv muaj kev tiv thaiv zoo rau ultraviolet hluav taws xob. Hauv qhov kev teeb tsa no, deoxyribonucleic acid muaj nyob hauv cov kab mob fungal.
Wet B-DNA
Nrog cov ntsev tsawg thiab muaj dej ntau, uas yog, nyob rau hauv cov xwm txheej ntawm lub cev, DNA xav tias nws lub ntsiab B. Cov molecules ntuj muaj nyob, raws li txoj cai, hauv B-daim ntawv. Nws yog nws leej twg underlies tus qauv Watson-Crick classical thiab feem ntau yog piav qhia hauv cov duab.
Daim ntawv no (nws tseem yog sab xis) yog qhov ua kom qis qis ntawm nucleotides (0.33 nm) thiab cov ntsia hlau loj (3.3 nm). Ib qho tig muaj 10.5 lub hauv paus khub, kev sib hloov ntawm txhua tus txheeb ze rau yav dhau los yog txog 36 °. Cov dav hlau ntawm cov khub yuav luag perpendicular rau lub axis ntawm "ob chav helix". Txoj kab uas hla ntawm ob txoj saw yog me dua li ntawm daim ntawv A - nws ncav cuag 2 nm xwb.
Non-canonical Z-DNA
Tsis zoo li canonical DNA, Z-hom molecule yog ib qho ntsia hlau sab laug. Nws yog qhov thinnest ntawm tag nrho cov, muaj ib txoj kab uas hla ntawm tsuas yog 1.8 nm. Nws cov coils, 4.5 nm ntev, zoo li elongated; Daim ntawv no ntawm DNA muaj 12 khub hauv paus ib zaug. Qhov kev ncua deb ntawm nucleotides uas nyob ib sab kuj loj heev - 0.38 nm. Yog li Z-puab muaj qhov sib tw tsawg tshaj plaws.
Nws yog tsim los ntawm B-hom teeb tsa hauv cov cheeb tsam uas muaj purinethiab pyrimidine hauv paus, nrog kev hloov pauv hauv cov ntsiab lus ntawm ions hauv kev daws. Kev tsim ntawm Z-DNA cuam tshuam nrog kev ua haujlwm lom neeg thiab yog cov txheej txheem luv luv. Daim ntawv no tsis ruaj khov, uas tsim teeb meem hauv kev kawm txog nws txoj haujlwm. Txog tam sim no, lawv tsis meej meej.
DNA replication thiab nws cov qauv
Ob qho tib si thawj thiab theem nrab ntawm DNA tshwm sim thaum lub sijhawm tshwm sim hu ua replication - tsim ntawm ob qhov zoo tib yam "ob chav helixes" los ntawm niam txiv macromolecule. Thaum lub sij hawm replication, tus thawj molecule unwinds, thiab complementary bases tsim nyob rau hauv lub tso tawm ib leeg chains. Txij li thaum DNA halves yog antiparallel, cov txheej txheem no ua rau lawv nyob rau hauv ntau cov lus qhia: nyob rau hauv kev sib raug zoo rau cov niam txiv chains ntawm lub 3'-kawg mus rau 5'-kawg, uas yog, tshiab chains loj hlob nyob rau hauv cov kev taw qhia 5' → 3'. Cov strand yog synthesized tsis tu ncua ntawm replication diav rawg; Nyob rau hauv lub lagging strand, synthesis yog ua los ntawm rab rawg nyob rau hauv nyias seem (Okazaki fragments), uas yog ces sewn ua ke los ntawm ib tug tshwj xeeb enzyme, DNA ligase.
Thaum qhov kev sib txuas txuas ntxiv mus, qhov kawg tsim ntawm tus ntxhais molecules tau raug helical twisting. Ces, ua ntej replication tiav, cov me nyuam mos molecules pib tsim ib tug tertiary qauv nyob rau hauv ib tug txheej txheem hu ua supercoiling.
Super Twisted Molecule
Daim ntawv supercoiled ntawm DNA tshwm sim thaum ob txoj hlua khi molecule ua rau kev sib tw ntxiv. Nws tuaj yeem ua clockwise (zoo) lossistawm tsam (qhov no ib tug hais txog qhov tsis zoo supercoiling). DNA ntawm cov kab mob feem ntau yog tsis zoo supercoiled, uas yog, tawm tsam lub ntsiab lem ntawm "ob chav helix."
Raws li qhov tshwm sim ntawm kev tsim cov voj voog ntxiv - supercoils - DNA tau txais ib qho kev teeb tsa nyuaj. Hauv eukaryotic hlwb, cov txheej txheem no tshwm sim nrog kev tsim cov complexes uas DNA coils tsis zoo nyob ib ncig ntawm histone protein complexes thiab siv daim ntawv ntawm cov xov nrog nucleosome hlaws. Cov seem dawb ntawm cov xov yog hu ua linkers. Non-histone proteins thiab inorganic compounds kuj koom nrog hauv kev tswj cov supercoiled zoo ntawm DNA molecule. Qhov no yog li cas chromatin tsim - cov khoom ntawm chromosomes.
Chromatin strands nrog nucleosomal hlaws muaj peev xwm ua rau muaj kev cuam tshuam ntxiv rau morphology hauv cov txheej txheem hu ua chromatin condensation.
Kawg compactization ntawm DNA
Nyob rau hauv lub nucleus, cov duab ntawm deoxyribonucleic acid macromolecule ua heev complex, compacting nyob rau hauv ob peb kauj ruam.
- Ua ntej, cov filament yog coiled rau hauv cov qauv solenoid tshwj xeeb - chromatin fibril 30 nm tuab. Nyob rau theem no, DNA folds thiab luv nws ntev li 6-10 npaug.
- Ntxiv mus, cov ntaub ntawv cov ntaub ntawv zigzag nrog kev pab los ntawm cov proteins tshwj xeeb scaffold, uas txo cov kab loj ntawm DNA twb dhau los ntawm 20-30 zaug.
- Densely packed loop domains are formed at the next level, feem ntau muaj cov duab conventionally hu ua "lamp txhuam". Lawv txuas rau cov protein intranuclearmatrix. Lub thickness ntawm cov qauv no twb 700 nm, thaum DNA yog luv luv los ntawm kwv yees li 200 zaug.
- Qib kawg ntawm lub koom haum morphological yog chromosomal. Lub voj domains yog compacted mus rau xws li ib tug raws li ib tug tag nrho shortening ntawm 10,000 lub sij hawm yog tiav. Yog tias qhov ntev ntawm cov molecule stretched yog li 5 cm, ces tom qab ntim rau hauv chromosomes nws yuav txo mus rau 5 microns.
theem siab tshaj ntawm cov teeb meem ntawm daim ntawv DNA mus txog hauv lub xeev metaphase ntawm mitosis. Nws yog tom qab ntawd nws tau txais cov yam ntxwv zoo li - ob lub chromatids txuas nrog lub constriction-centromere, uas ua kom lub divergence ntawm chromatids nyob rau hauv tus txheej txheem ntawm kev faib. Interphase DNA tau teeb tsa mus rau qib sau npe thiab muab faib rau hauv lub cell nucleus tsis muaj kev txiav txim tshwj xeeb. Yog li, peb pom tias morphology ntawm DNA yog ze ze rau ntau theem ntawm nws lub neej thiab qhia txog cov yam ntxwv ntawm kev ua haujlwm ntawm qhov tseem ceeb tshaj plaws rau lub neej.
