Mienzaniso yeMibvunzo Inokurukura Kurongeka kana Kuiswa kweDNA muMasero
Pengantar
DNA, kana kuti deoxyribonucleic acid, ndiyo molecule inotakura ruzivo rwemajini muzvinhu zvipenyu. Mukati memasero, DNA inofanira kurongedzwa zvakanaka kuti ikwane munucleus diki uku ichiramba iri nyore kushandisa pakuita zvinhu zvakakosha zvakaita sekukopa nekudhindisa. Kurongedzwa kweDNA nekurongedza uku kunosanganisira zvikamu zvakawanda nemaumbirwo, kusanganisira mapuroteni ehistone nechromatin. Muchinyorwa chino, tichakurukura mienzaniso yematambudziko ane chekuita nekurongedzwa kweDNA nemhinduro dzawo.
Mubvunzo 1: Tsanangura kuti DNA inounganidzwa sei munucleus yemasero eukaryotic.
Jawaban:
Kurongedza kwakaomarara kweDNA kunotanga nekuumbwa kwezvimiro zvinonzi nucleosomes. Nucleosomes ndiwo mayuniti ekutanga ekurongeka kwechromatin, ane chikamu cheDNA chinosvika 147 base pairs refu chakaputirwa pamapuroteni masere ehistone. Histones mapuroteni madiki, ane positive charge anobvumira DNA ine negative charge kuti iungane zvakasimba paari.
Nucleosome yega yega yakabatana nechikamu chipfupi che linker DNA, chakafanana ne "mabeads patambo." Kana mazinga aya ekurongedza akabatanidzwa, chimiro chacho chinowedzerwa kuunganidzwa mu chromatin fiber yakakora, ine upamhi hweinenge 30 nm, inozivikanwa se solenoid kana zigzag.
Ma solenoid anozopetwazve nerubatsiro rwema scaffold proteins kuita densive structures, zvichizopedzisira zvaita ma chromosomes anoonekwa panguva yekupatsanurwa kwemasero. Munguva ye interphase, chromatin inogona kuwanikwa mu heterochromatin (yakaomarara zvakanyanya uye kazhinji isingashandi mu transcription) uye euchromatin (isina kunyanya kuomarara uye inoshanda mu transcription).
Mubvunzo 2: Zvinodzora kana kugadzirisa histone zvinoita sei basa rekudzora magene?
Jawaban:
Histones dzinogadziriswa zvakasiyana-siyana zvemakemikari, zvakaita semethylation, acetylation, phosphorylation, uye ubiquitination, izvo zvinoita basa guru mukugadzirisa kutaura kwemajini. Kugadziriswa uku kunogona kukanganisa kuti chromatin yakasununguka kana kuti yakavharidzirwa sei, nokudaro zvichikanganisa kuwanikwa kweDNA kumichina yekunyora:
1. Histone Acetylation: Kuwedzerwa kwemapoka eacetyl kuhistone lysine residues nema enzymes ehistone acetyltransferase (HAT) kunoderedza simba rakanaka rehistones, nokudaro zvichideredza kushanda kwawo neDNA uye zvichikonzera chromatin yakareruka. Loose chromatin inobvumira kuwana nyore nyore transcription factors, nokudaro zvichiwedzera gene expression.
2. Histone Methylation: Kuwedzerwa kwemapoka emethyl kunogona kumutsa kana kudzvinyirira kugadzirwa kwemajini zvichienderana nenzvimbo uye mamiriro ezvisaririra zvemethylated. Semuenzaniso, H3K4 methylation inowanzobatanidzwa nekushandiswa kwemajini, nepo H3K9 neH3K27 methylation zvichibatanidzwa nekudzvinyirirwa kwemajini.
3. Phosphorylation Nemamwe Magadzirirwo: Mamwe magadzirirwo ehistone anobatsirawo muchimiro uye mashandiro echromatin, kazhinji kana tichitarisa mhinduro dzemasero uye kutenderera kwemasero.
Kazhinji, kugadziriswa kwehistone kunopa "histone code" inoratidza mamiriro ekutaura kwemajini mamwe musero uye inopindura kuchinja kwezvakatipoteredza kana mamiriro emasero.
Mubvunzo 3: Mukuyedza, chidimbu cheDNA chakawanikwa chine urefu hwe10.000 bp. Mushure mekupatsanurwa nekuongororwa, chidimbu chacho chakawanikwa chine manucleosome makumi mashanu. Zvichibva paruzivo urwu, ndeapi avhareji yehurefu hwe linker DNA pakati pemanucleosome ari muchidimbu ichi?
Jawaban:
Kuti tigadzirise dambudziko iri, tinofanira kuziva kuti nucleosome yega yega inotenderera 147 bp yeDNA. Saka, kana paine nucleosomes makumi mashanu, hurefu hwese hweDNA hwakatenderedzwa nenucleosome ndehwekuti:
\[ 147 \text{ bp/nucleosome} \times 50 \text{ nucleosomes} = 7350 \text{ bp} \]
Kureba kwese kweDNA i10.000 bp, saka huwandu hwese hweDNA yekubatanidza ndeinotevera:
\[ 10.000 \text{ bp} – 7350 \text{ bp} = 2650 \text{ bp} \]
Sezvo paine ma linkers makumi mana nemapfumbamwe (linker DNA pakati pema nucleosome maviri), avhareji yehurefu hwe linker DNA imwe chete ndeiyi:
\[ \frac{2650 \text{ bp}}{49} \approx 54.08 \text{ bp} \]
Saka, avhareji yehurefu hwe linker DNA pakati pe nucleosome yega yega inenge 54 bp.
Mhedziso
Kurongedza DNA mukati memasero inzira yakaoma uye inodzorwa zvakanyanya, zvichiita kuti kuchengetwa kwemashoko ezvemajini kubudirire uye kuti michina yemorekuru iwanikwe zvakanaka. Ruzivo rwekurongeka kweDNA, kusanganisira chimiro chenucleosome uye shanduko dzehistone, rwakakosha pakunzwisisa kutonga kwemajini uye mashandiro emasero. Mienzaniso yakakurukurwa pamusoro apa inopa kunzwisisa kwakadzama kwekuti DNA inorongedzwa sei uye yakarongwa sei mukati menucleus, ukuwo tichiwedzera kunzwisisa kwedu biology yemamorekuru.
