Ukuhlelwa kwe-DNA noma Ukupakishwa Kwamaseli
Ezingeni lama-molecule, ukuphila eMhlabeni kwakhelwe esisekelweni solwazi lwezakhi zofuzo oluqukethwe kuma-molecule e-DNA. I-DNA, noma i-deoxyribonucleic acid, iyi-polymer egcina imiyalelo yezinto eziphilayo ebalulekile ekuthuthukisweni, ekusebenzeni, ekukhuleni nasekuzaleni kwazo zonke izinto eziphilayo. Nakuba i-DNA yakhiwe izinhlobo ezine kuphela zama-nucleotide—i-adenine (A), i-thymine (T), i-cytosine (C), kanye ne-guanine (G)—ukuhleleka kwazo ngaphakathi kwamaseli kuyinkimbinkimbi kakhulu. Ake sihlole ngokuningiliziwe ukuthi i-DNA ihlelwe kanjani, noma ipakishwe kanjani, ngaphakathi kwamaseli.
Isakhiwo Esiyisisekelo se-DNA
I-DNA inesimo se-double helix, esatholwa nguJames Watson noFrancis Crick ngo-1953. Lesi sakhiwo sifana neladi elisontekile, elinamabhangqa ayisisekelo njengama-rungs kanye nomgogodla we-sugar-phosphate njengezibambo. Amabhangqa ayisisekelo phakathi kwe-adenine ne-thymine, kanye ne-cytosine ne-guanine, axhunywe ngezibopho ze-hydrogen, okunikeza ukuzinza kwe-double helix.
Ama-Histones nama-Nucleosomes
Ku-nucleus yeseli le-eukaryotic, i-molecule ye-DNA ingaba amamitha amaningana ubude uma inwetshiwe ngokuphelele. Ukufaka le molecule enkulu kuyi-nucleus ene-micrometer ezimbalwa kuphela ububanzi kudinga indlela eyinkimbinkimbi yokupakisha. Esinye isici esibalulekile sokupakisha i-DNA amaprotheni abizwa ngokuthi ama-histone.
Ama-Histones amaprotheni ayisisekelo acebile ngama-amino acid i-lysine ne-arginine, okuwavumela ukuthi asebenzisane kahle ne-DNA ene-asidi. I-DNA izungezwe ama-histones, yakha izakhiwo ezaziwa ngokuthi ama-nucleosomes. I-nucleosome ngayinye iqukethe cishe ama-base pair angu-147 e-DNA azungezwe iqembu lama-histones ayisishiyagalombili, akha iyunithi eyisisekelo yokupakisha ye-chromatin. Lolu chungechunge lwama-nucleosomes lufana "nentambo yama-beads" ngaphansi kwe-microscope.
I-Chromatin nama-Chromosomes
Ukupakishwa kwe-DNA kuyaqhubeka emazingeni aphezulu, lapho ama-nucleosome ehlelwa khona abe yisakhiwo esincinyane nesihlelekile esibizwa ngokuthi i-chromatin. Kunezinhlobo ezimbili eziyinhloko ze-chromatin: i-euchromatin kanye ne-heterochromatin. I-Euchromatin iyindlela evulekile futhi esebenzayo kakhulu yokubhala, okusho ukuthi i-DNA kulezi zindawo ifinyeleleka kalula emishinini yokubhala. Ngokuphambene nalokho, i-heterochromatin incinyane kakhulu futhi ivame ukuhlotshaniswa ne-DNA engasebenzi yokubhala.
Ukuhleleka okwengeziwe kwakha ama-chromosome, izakhiwo ezisezingeni eliphezulu kakhulu zokupakishwa kwe-DNA, ezibonakala ngesikhathi sokuhlukaniswa kwamaseli. Ama-chromosome ayifomu elincane kakhulu le-DNA futhi aqinisekisa ukuphindaphindwa kwe-DNA okunembile ngaphandle kokulahlekelwa izingxenye ezibalulekile ngesikhathi se-mitosis kanye ne-meiosis. Abantu, isibonelo, banama-chromosome angu-46 kuseli ngalinye lomzimba.
Umthetho Wokupakisha i-DNA
Ukupakishwa kwe-DNA akuyona inqubo engaguquki; iyashintshashintsha futhi ithonywa izici ezahlukahlukene. Ukuguqulwa kwe-Histone, njenge-acetylation, i-methylation, i-phosphorylation, kanye ne-ubiquitination, kungashintsha ukusebenzisana phakathi kwe-DNA nama-histone, ngaleyo ndlela kuthinte ukuminyana kwe-chromatin kanye nokufinyeleleka kwe-DNA ekubhalweni. Isibonelo, i-histone acetylation ngokuvamile ihlotshaniswa ne-euchromatin kanye ne-active transcription, kuyilapho i-methylation ingadlala indima ekwakhiweni kwe-heterochromatin.
Ngaphezu kwama-histone, kukhona namaprotheni okuvuselela i-chromatin angashukumisa, anciphise, noma ahlele kabusha izikhundla ze-nucleosome, okuthuthukisa ukufinyeleleka kwezakhi zofuzo. Zonke lezi zici zisebenza ndawonye ukuze kuthuthukiswe ukulawulwa kwe-DNA ukuze kuhlangatshezwane nezidingo zamaseli aguqukayo.
Ukupakishwa kwe-DNA kuma-Prokaryotes
Ngokungafani nama-eukaryotes, amabhaktheriya nezinye izinto eziphilayo ze-prokaryotic ngokuvamile zine-DNA eyindilinga, hhayi eqondile, futhi azinawo i-nucleus eboshwe ulwelwesi. Nakuba kulula, ukupakishwa kwe-DNA kuma-prokaryotes akubalulekile kangako. Kumabhaktheriya, i-DNA ihlanganiswa ngosizo lwamaprotheni afana ne-HU ne-IHF, aqinisa i-supercoiling futhi alawule isakhiwo se-nucleoid.
Ukubaluleka Kokupakishwa Kwe-DNA
Ukupakishwa kwe-DNA okuphumelelayo akukhona nje ukugcina ulwazi lwezakhi zofuzo, kodwa futhi nokulawula ukusebenza kwezakhi zofuzo. Indawo kanye nobuningi be-chromatin kungathonya ukuvezwa kwezakhi zofuzo, futhi ngenxa yalokho, kuyisici esibalulekile ocwaningweni oluningi ku-epigenetics. Ucwaningo lwamamodeli e-epigenetic lunganikeza ukuqonda ngezimo nezifo ezahlukahlukene zempilo, okuhlanganisa umdlavuza kanye nezinkinga zokukhula.
Isibonelo, izinguquko emaphethini okupakisha i-DNA zingaholela ekubonakalisweni kwezakhi zofuzo okungavamile, okuhlobene nokukhula komdlavuza. Izindlela zokwelapha eziqondisa ukuguqulwa kwe-histone noma isakhiwo se-chromatin zibonisa amandla ekwelapheni izifo ezibangelwa ukulawulwa kwe-epigenetic okuphazamisekile.
Isiphetho
Ukulawulwa noma ukupakishwa kwe-DNA ngaphakathi kwamaseli kuyinqubo eyinkimbinkimbi nenemininingwane edlala indima ebalulekile empilweni. Ukupakishwa kwe-DNA akugcini nje ngokuthonya ukuzinza kwezakhi zofuzo ngesikhathi sokuhlukaniswa kwamaseli kodwa futhi kusebenza njengomlawuli oyinhloko, olawula ukuthi yiziphi izakhi zofuzo ezivezwa ngesikhathi esifanele nangenani elifanele. Ukuqonda imininingwane yokupakishwa kwe-DNA kunikeza ukuqonda okujulile ngezisekelo zebhayoloji yamaseli futhi kuvula indlela yokuthuthukiswa kwezindlela zokwelapha ezintsha zezifo zezakhi zofuzo kanye ne-epigenetic. Njengenye yezimfihlakalo ezithakazelisa kakhulu kubhayoloji yama-molecule, ucwaningo kulo mkhakha luzoqhubeka nokunikeza izinselele namathuba ajabulisayo kososayensi emhlabeni wonke.
