Okukwenza Ube “Nguwe”

NGAPHAMBI kokuba kuqale i-Human Genome Project, ososayensi base befunde okuningi ngokwakheka kwezici zethu zofuzo. Yingakho amagama anjengelithi “izakhi zofuzo,” “ama-chromosome,” nelithi “DNA” evela njalo emibikweni yezindaba njengoba imithombo yezindaba imemezela ukutholakala kwezinto eziningi zalokho abacwaningi abakholelwa ukuthi kusenza sibe yilokho esiyikho. I-Human Genome Project manje izama ukwakhela kulezizisekelo futhi ihlaziye konke ukwakheka kwezici zethu zofuzo.

Ngaphambi kokuba sicabangele indlela ososayensi abakwenza ngayo lokhu, siza ufunde ibhokisi elithi “Ipulani Yezakhi Zakho Zofuzo,” ekhasini 6 lalomagazini.

Ukuthola Izakhi Zofuzo

Njengoba kushiwo esihlokweni esandulele, inhloso yokuqala ye-Human Genome Project ibiwukuthola ukuthi izakhi zethu zofuzo zitholakalaphi kuma-chromosome ethu. Umcwaningi othile wezakhi zofuzo ufanisa lokhu “nokufuna isibani esifile endlini engenalo ikheli emgwaqweni ongaziwa edolobheni elindawana-thile ezweni ongalazi.” Umagazini i-Time uthi lomsebenzi “unzima njengokufuna inombolo yocingo ungenalo ikheli noma isibongo.” Ososayensi bayisingatha kanjani-ke lenselele?

Abacwaningi bahlola imikhaya ukuze bathole izakhi zofuzo ezinquma izici ezidluliselwa ngofuzo nemikhuba kanye nokuthambekela okwaziwa kahle. Ngokwesibonelo, baye bathola izakhi zofuzo ezenza umuntu angakwazi ukuhlukanisa imibala, ezibangela ukopha ngokweqile, nezakha ulwanga ezindaweni ezithile kwenye yama-chromosome ethu. Lokhu kwakheka kwezici ezihlobene nezakhi zofuzo akunembile—kuphawula indawo yesakhi sofuzo kuphela phakathi kwezisekelo ezibhangqiwe ezingaba yizigidi ezinhlanu.

Ukuze banembe ngokwengeziwe, ososayensi bahlose ukuqoqa ukuhlaziywa okungokoqobo. Kwenye inqubo, bahlukanisa izingxenye ze-DNA zibe izingcezu ezingalingani bese bezihlaziya ukuze bathole ukulandelaniswa kwezakhi zofuzo ezikhethekile. Yiqiniso, lapho kunezingcezu eziningi, kulapho kuba nzima nakakhulu ukuzihlela. Uma uqhathanisa ingxenye ngayinye ye-DNA nencwadi eseshalofini lomtapo ophawulwe kahle, khona-ke ukuthola isakhi sofuzo kufana “nokuthola ingcaphuno encwadini eyodwa kunokuba uhlole kuwo wonke umtapo,” kuchaza umagazini i-New Scientist. Lokhu kuhlaziywa okungokoqobo kunciphisa indawo ehlolwayo ibe nezisekelo ezibhangqiwe ezingu-500 000. Ngasekupheleni kuka-1993, iqembu lososayensi elaliholwa uDkt. Daniel Cohen e-Center for the Study of Human Polymorphism eParis, eFrance, lakhiqiza lokho umagazini i-Time owakubiza ngokuthi “ukuhlaziywa kokuqala okugcwele—nakuba kunganembile—kwe-genome yomuntu.”

Umgomo olandelayo walomkhankaso uwukuhlela ukulandelana okunembile kwengxenye ngayinye yamakhemikhali ezakhi zethu zofuzo ezingu-100 000, kanye nezinye izingxenye ze-genome. Kodwa njengoba ososayensi bethuthukisa amakhono abo okufunda i-DNA, bathola ukuthi i-genome iyinkimbinkimbi kakhulu kunendlela ababecabange ngayo.

Ukufunda I-genome

Izakhi zofuzo zakha amaphesenti amabili kuya kwamahlanu kuphela e-genome yethu. Konke okunye ngokuvamile kubizwa ngokuthi “i-DNA engabalulekile.” Abanye abacwaningi babecabanga ukuthi lokhu okubizwa ngokuthi ukulandelaniswa okungenalusizo kwakheka ngengozi phakathi nokuziphendukela kwemvelo. Manje bakholelwa ukuthi ezinye zalezizingxenye ezingenazo izakhi zofuzo zilawula ukwakheka kwe-DNA futhi ziqukethe iziyalezo ezidingwa ama-chromosome ukuze ande phakathi nokuhlukana kwamangqamuzana.

Sekuyisikhathi eside abacwaningi benesithakazelo kulokho okwenza isakhi sofuzo sisebenze noma singasebenzi. I-New Scientist ibika ukuthi kungenzeka kunezakhi zethu zofuzo ezingaba ngu-10 000 ezibangela ukuba kukhiqizwe amaprotheni abizwa ngokuthi izici ezilawulayo. Cishe idlanzana lalezizici liyahlangana bese lingena emseleni we-DNA njengokhiye engidini. Lapho sezingenile zishukumisa isakhi sofuzo esiseduze noma zicindezele ukusebenza kwaso.

Bese kuba khona izakhi zofuzo ezibizwa ngokuthi ama-stuttering gene ezinezingxenye zomthetho wamakhemikhali eziphindwe kaningi. Esinye salezizakhi ngokuvamile sine-CAG triplet—uxhaxha lwama-nucleotide amathathu olwenza i-amino acid ngayinye ihluke—ephindeke izikhathi eziphakathi kuka-11 no-34. Lapho iphindeka izikhathi ezingu-37 noma ngaphezulu, ibangela ukuphazamiseka okubi kobuchopho okubizwa ngokuthi i-Huntington’s chorea.

Cabangela futhi nomphumela wokushintsha kohlamvu esakhini sofuzo. Uhlamvu oluyiphutha ohlelweni lwezinhlamvu ezingu-146 zengxenye eyodwa kwezimbili ze-hemoglobin lubangela i-sickle-cell anemia. Noma kunjalo, umzimba unesimiso sokuhlaziya esihlola ukunemba kwe-DNA lapho amangqamuzana ehlukana. Kubikwa ukuthi iphutha elilodwa kulesisimo lingabangela umdlavuza kapopopo. Ezinye izifo eziningi, njengesifo sikashukela nesenhliziyo, nakuba zingewona nje umphumela wephutha elilodwa lezakhi zofuzo, zisabangelwa ukusebenzelana kwezakhi zofuzo eziningi ezinephutha.

Ukushintsha I-genome

Odokotela bathembele kuyi-Human Genome Project ukuze bathole ukwaziswa okuyobasiza ukuba baxilonge futhi belaphe izifo zomuntu. Kakade sebesungule ukuhlola okwembula amaphutha ekulandelaneni kwezinye izakhi zofuzo. Abanye bakhathazeka ngokuthi abantu abangenazimiso bayosebenzisa ukuhlola izakhi zofuzo ukuze bafeze inqubo yokuthuthukisa izimfanelo zofuzo. Okwamanje abaningi bamelene nokwelashwa kombungu, okuhilela ukushintshwa kwezakhi zofuzo zesidoda nengqamuzana yeqanda. Ngisho nemibhangqwana ecabangela ukukhuliselwa ngaphandle kwesibeletho kombungu onezakhi zofuzo eziphilile kumelwe ibhekane nezinqumo zokuthi kwenziwani ngaleyomibungu engakhethwanga ukuba ibuyiselwe esibelethweni. Ngaphezu kwalokho, abantu abacabangayo bazwakalisa ukukhathazeka ngomphumela wokuxilonga okwembula iphutha elisobala ezakhini zofuzo kumntwana ongakazalwa. Abaningi bakhathazwa ukwesaba ukuthi ukuhlaziywa kwezakhi zofuzo kubantu abadala kuyoshintsha indlela abaqashwa ngayo, abakhushulelwa ngayo esikhundleni, ngisho nabanikezwa ngayo umshuwalense. Kukhona-ke nendaba ekhathazayo yokuqondiswa kwezakhi zofuzo.

“Benganelisiwe ukufunda incwadi yokuphila,” kuphawula i-Economist, “bafuna nokubhala kuyo.” Enye indlela odokotela abangase bakwazi ngayo ukukwenza lokhu iwukusebenzisa ama-retrovirus. I-virus ingase ibhekwe njengeqembu lezakhi zofuzo esakeni lamakhemikhali. Beqala nge-virus ehlasela abantu, ososayensi basusa izakhi zofuzo ezidingwa yile-virus ukuze izandise futhi esikhundleni sazo bafake ingxenye ephilile yezakhi zofuzo zesiguli ezinephutha. Lapho isifakwe emzimbeni, le-virus ihlasela amangqamuzana ethunyelwe kuwo futhi esikhundleni sezakhi zofuzo ezinephutha ifake eziphilile eziphethe.

Ngokusekelwe ekutholakaleni kwesakhi sofuzo esingavikela emdlavuzeni wesikhumba, muva nje ososayensi babike indlela yokwelapha elula. Njengoba kungumuntu oyedwa kuphela kwabangu-20 onalesisakhi sofuzo, injongo iwukusifaka kukhilimu oyofaka lesisakhi sofuzo emangqamuzaneni esikhumba. Lapho lesisakhi sofuzo sishukumisa ukukhiqizwa kwe-enzyme odokotela abakholelwa ukuthi ibhidliza ubuthi obubangela umdlavuza obuhlasela umzimba.

Nakuba lezizinqubo zimangalisa kangaka, imithetho eqinile ilinganisela ukusetshenziswa kokuqondiswa kwezakhi zofuzo njengoba ososayensi belwisana nokukhathazeka komphakathi ngemiphumela yakho engase ivele.

Kuningi okusazotholwa ngobunkimbinkimbi be-genome yomuntu. Ngempela, “ayikho i-genome eyodwa yomuntu,” kuphawula isazi sezakhi zofuzo uChristopher Wills. “Ayizigidi eziyizinkulungwane ezinhlanu, cishe eyodwa kuwo wonke umuntu okuleplanethi.” I-genome yakho yembula okuningi ngawe. Kodwa ingabe ikwembula konke?

Ingabe I-genome Yakho Ikwembula Konke?

Abanye bacabanga ukuthi izakhi zofuzo zingomashiqela abancane abasenza siziphathe ngendlela esiziphatha ngayo. Eqinisweni, imibiko yezindaba yamuva nje imemezele ukutholakala kwezakhi zofuzo abanye abakholelwa ukuthi zibangela ukuphazamiseka kwengqondo, ukuluthwa utshwala, ngisho nobungqingili. Ososayensi abaningi baluleka ukuba kuqashelwe lokhu kuhlobana. Ngokwesibonelo, umlobi uChristopher Wills ubhala ukuthi kwezinye izimo ukushintsha kwezakhi zofuzo kumane “kuchaye abanakho ekuluthweni utshwala.” Ngokwe-Times yaseLondon, isazi sezakhi zofuzo zama-molecule uDean Hamer saveza umbono wokuthi izici zomuntu zobulili ziyinkimbinkimbi ngokweqile ukuba zinganqunywa isakhi esisodwa sofuzo. Ngempela, i-1994 Britannica Book of the Year iyabika: “Nokho, asikho isakhi sofuzo esakhonjwa njengesibangela ubungqingili, futhi umsebenzi osewenziwe kuze kube manje kungadingeka ukuba uqinisekiswe abanye.” Ngaphezu kwalokho, umagazini i-Scientific American uyaphawula: “Imikhuba yokuziphatha kunzima ngokungavamile ukuyichaza, futhi cishe konke okushiwo ngesisekelo sezakhi zofuzo kungachazwa futhi njengomphumela wendawo ezungezile.”

Ngokuthakazelisayo, ohlelweni lwethelevishini i-BBC oluthi Cracking the Code, isazi sezakhi zofuzo uDkt. David Suzuki saveza inkolelo yokuthi “izimo zethu ngabanye, inkolo yethu, ngisho nobulili bethu kungayishintsha indlela izakhi zethu zofuzo ezisithinta ngayo. . . . Indlela izakhi zofuzo ezisithinta ngayo ixhomeke ezimweni zethu.” Ngenxa yalokho, siyaxwayisa: “Uma ufunda emaphephandabeni ukuthi ososayensi bathole isakhi sofuzo esibangela ukuluthwa utshwala, noma ubugebengu, noma ukuhlakanipha, noma ngabe yini, ungakwamukeli ngokuphelele. Ukuze bachaze ukuthi isakhi esithile sofuzo simthinta kanjani umuntu, ososayensi kungadingeka bazi zonke izinto nangendawo ezungezile yalowomuntu, futhi ngisho nalokho kungase kunganeli.”

Ngempela kunjalo, ngoba esinye futhi isici singathonya lokho oyikho. Isihloko esilandelayo sicabangela ukuthi lesi siyini nokuthi singakuthonya kanjani ngendlela ekuzuzisayo.

[Ibhokisi/Umdwebo ekhasini 6, 7]

(Ukuze ubone ukuthi indaba ihlelwe kanjani, bheka encwadini)

Ipulani Yezakhi Zakho Zofuzo

• Umzimba wakho unamangqamuzana angaba yizigidi zezigidi eziyikhulu, amaningi awo aqukethe ipulani ephelele yezakhi zakho zofuzo. (Nokho, amangqamuzana abomvu egazi lakho awanayo i-nucleus futhi ngenxa yalokho awanayo ipulani yezakhi zofuzo.)

• Amangqamuzana akho ayinkimbinkimbi, njengamadolobha anezimboni, izikhungo zokugcina imithombo yamandla, kanye nemizila emisiwe yokungena nokuphuma. Iziqondiso zivela kuyi-nucleus yengqamuzana.

• I-nucleus yengqamuzana yakho, isizinda sepulani yezakhi zakho zofuzo, ingafaniswa nehholo ledolobha, lapho iziphathimandla zikahulumeni wendawo ngokuvamile zigcina khona amapulani ezakhiwo ezikuleyondawo. Ukuze zakhiwe, othile kufanele a-ode izinto zokwakha, alungiselele amathuluzi nemishini yomsebenzi, futhi ahlele abakhi.

• Ama-chromosome akho acacisa ipulani yezakhi zakho zofuzo. Lama-molecule e-DNA asongekile abhangqwe aba ngu-23, uma esonjululwa bese exhunyaniswa, angafinyelela enyangeni futhi abuye izikhathi ezingaba ngu-8 000!

• I-DNA yakho inezinhlangothi ezihlanganiswe izingxenye zamakhemikhali ezibhangqiwe ezibizwa ngokuthi izisekelo, njengezikhwelo zesitebhisi kodwa okuyisitebhisi esisontekile. I-adenine (A) eyisisekelo ngaso sonke isikhathi ihlangana ne-thymine (T), i-cytosine (C) ihlangane ne-guanine (G). Uma uhlukanisa le-DNA enjengesitebhisi ngendlela obungavula ngayo uziphu, wembula isimiso sezakhi zofuzo esibhalwe kulezozinhlamvu ezine, u-A, C, G, no-T.

• Ama-ribosome akho, njengezimboni ezihambayo, ayazinamathisela ukuze afunde isigijimi esibhalwe kuyi-RNA (ribonucleic acid). Njengoba enza kanjalo, abopha ndawonye izakhi ezihlukahlukene ezibizwa ngokuthi ama-amino acid, ezakha amaprotheni akwenza ube “nguwe.”

• Izakhi zakho zofuzo ziyizingxenye ze-DNA enezakhi zokwakha izakhi zomzimba, amaprotheni. Lezizakhi zofuzo zinquma ithuba lokungenwa kwakho izifo ezithile. Ukuze afunde izakhi zakho zofuzo, amathuluzi angamakhemikhali abizwa ngokuthi ama-enzyme avula ibhande le-DNA. Amanye ama-enzyme abe “esefunda” isakhi sofuzo, akhe kuso uchungechunge oluphelelisayo lwezisekelo ngesilinganiso sezingu-25 ngomzuzwana.

[Ibhokisi/Isithombe ekhasini 8]

Umdwebo Wesakhi Sofuzo

Khipha i-DNA ethile esicutshini somuntu bese usihlukanisa sibe izicucwana. Faka lezizicucwana kuyi-gel, dlulisa amandla kagesi, bese ucwilisa amabala avelayo olwebwini lwe-nylon. Faka uthi olukhipha imisebe lokuhlola izakhi zofuzo, bese uthatha isithombe. Umphumela isigxivizo se-DNA.