{"id":16297,"date":"2016-02-01T16:46:14","date_gmt":"2016-02-01T14:46:14","guid":{"rendered":"http:\/\/109.232.216.219\/~bilimvegelecek\/?p=16297"},"modified":"2018-01-09T16:54:04","modified_gmt":"2018-01-09T13:54:04","slug":"cop-dna","status":"publish","type":"post","link":"https:\/\/bilimvegelecek.com.tr\/index.php\/2016\/02\/01\/cop-dna","title":{"rendered":"\u00c7\u00f6p DNA"},"content":{"rendered":"

\u00c7\u00f6p DNA\u2019n\u0131n, at\u0131l ve etkisiz DNA dizilerinden olu\u015fmad\u0131\u011f\u0131 anla\u015f\u0131l\u0131yor. Onlardan art\u0131k \u00e7\u00f6p DNA de\u011fil de \u2018kodlamayan DNA\u2019 (noncoding DNA) \u015feklinde s\u00f6z edilmesi, bu anlay\u0131\u015f\u0131n yayg\u0131nla\u015ft\u0131\u011f\u0131n\u0131 g\u00f6steriyor. Kromozomlar\u0131m\u0131z\u0131n bu \u2018karanl\u0131k madde\u2019sinin ara\u015ft\u0131rmac\u0131lar\u0131 daha uzun y\u0131llar me\u015fgul edece\u011fi \u015f\u00fcphesiz. Hi\u00e7 beklenmedik sonu\u00e7lara haz\u0131r olal\u0131m! <\/em><\/p>\n

2000\u2019li y\u0131llar\u0131n ba\u015flar\u0131nda, insan genomunun dizilenmesi, insan akl\u0131n\u0131n ve bilimin en b\u00fcy\u00fck zaferlerinden biri olarak ilan edilip kutland\u0131. \u0130nsano\u011flu, art\u0131k hayat\u0131n s\u0131rr\u0131n\u0131 \u00e7\u00f6zm\u00fc\u015ft\u00fc. ABD ba\u015fkan\u0131 Bill Clinton\u2019un beyan\u0131, d\u00fcnya kamuoyunda geni\u015f yank\u0131 buldu: \u201cBug\u00fcn, Tanr\u0131\u2019n\u0131n ya\u015fam\u0131 yarat\u0131rken kulland\u0131\u011f\u0131 dili \u00f6\u011freniyoruz.\u201d<\/p>\n

\"\"Oswald Avery\u2019nin genetik materyalin ta\u015f\u0131y\u0131c\u0131s\u0131n\u0131n proteinler de\u011fil de DNA oldu\u011funu 1944 y\u0131l\u0131nda g\u00f6stermesinden sonra, insan kromozomunun s\u0131rr\u0131n\u0131 \u00e7\u00f6zmek ve gen haritas\u0131n\u0131 \u00e7\u0131karmak bilim d\u00fcnyas\u0131n\u0131n en \u00f6nemli hedeflerinden biri olmu\u015ftu. (Hat\u0131rlatal\u0131m: kromozom, DNA zincirinin \u201chiston\u201d ad\u0131 verilen proteinler etraf\u0131na sar\u0131l\u0131p olu\u015fturdu\u011fu yap\u0131n\u0131n ad\u0131d\u0131r. DNA zinciri ise esasen d\u00f6rtl\u00fc bir \u2018alfabe\u2019den olu\u015fur: harfleri A, C, G ve T olan bir alfabe. Bu harfler, her birine \u2018baz\u2019 denilen d\u00f6rt molek\u00fcl ad\u0131n\u0131n k\u0131saltmas\u0131d\u0131r asl\u0131nda: A adenin, C sitozin (cytozin), G guanin ve T timin ad\u0131yla bilinen molek\u00fcller.)<\/p>\n

Ba\u015fkan Clinton\u2019un m\u00fcjdecisi oldu\u011fu tarihi ba\u015far\u0131, bilim d\u00fcnyas\u0131nda m\u00fcthi\u015f bir i\u015fbirli\u011fi ama ayn\u0131 zamanda da k\u0131ran k\u0131rana ge\u00e7en bir rekabet sonucu ortaya \u00e7\u0131km\u0131\u015ft\u0131. ABD, \u0130ngiltere, Fransa, Almanya, Japonya ve \u00c7in\u2019de y\u00fcr\u00fct\u00fclen t\u00fcm ara\u015ft\u0131rmalar\u0131n maliyeti 3 milyar dolar mertebesindeydi. Bu arada son 15 y\u0131lda, bilgisayar tabanl\u0131 dizileme tekniklerinde ola\u011fan\u00fcst\u00fc ilerlemeler ge\u00e7ekle\u015ftirildi. O kadar ki, bir insan genomunu dizilemenin fiyat\u0131 2001 y\u0131l\u0131nda yakla\u015f\u0131k 100 milyon dolar iken, g\u00fcn\u00fcm\u00fczde sadece bin dolar civar\u0131ndad\u0131r. Genom yap\u0131s\u0131n\u0131 ucuza dizileyebilmenin \u00f6nemi, ki\u015fiden ki\u015fiye farkl\u0131l\u0131k g\u00f6steren genomu her birey i\u00e7in belirlemek suretiyle \u00f6zel tedavilerin \u00f6n\u00fcn\u00fcn a\u00e7\u0131lmas\u0131ndan kaynaklanmaktad\u0131r (\u00f6rne\u011fin kanser tedavisinde, hastan\u0131n t\u00fcm\u00f6rl\u00fc h\u00fccrelerini dizileyerek kanserin ilerleyi\u015fini tetikleyen mutasyonlar\u0131 anlamak m\u00fcmk\u00fcn olabiliyor).<\/p>\n

Gen say\u0131s\u0131 bilmecesi ve karma\u015f\u0131kl\u0131k<\/strong><\/p>\n

\u0130nsan DNA\u2019s\u0131n\u0131n dizilenmesinden \u00f6nce, daha \u00e7ok vir\u00fcs ile bakteriler olmak \u00fczere \u00e7ok say\u0131da organizman\u0131n genomu dizilenmi\u015fti bile. Ancak biyolojik olarak en karma\u015f\u0131k varl\u0131klardan biri oldu\u011fu d\u00fc\u015f\u00fcn\u00fclen insan\u0131n \u00e7ok y\u00fcksek say\u0131da gene sahip olmas\u0131 gerekti\u011fi de yayg\u0131n bir kanaatti. Pek \u00e7ok biliminsan\u0131n\u0131n tahminine g\u00f6re insan gen say\u0131s\u0131, 30 bin ile 100 bin aras\u0131nda olmal\u0131yd\u0131.<\/p>\n

Dizileme \u00e7al\u0131\u015fmalar\u0131, biri \u0130nsan Genomu Projesi olarak uluslararas\u0131 bir i\u015fbirli\u011fi \u00e7at\u0131s\u0131 alt\u0131nda, di\u011feri ise \u00f6zel bir kurulu\u015f olan Celera Genomics\u2019e ait bir proje \u00e7er\u00e7evesinde, iki ayr\u0131 grup taraf\u0131ndan y\u00fcr\u00fct\u00fcld\u00fc. Bu iki grubun \u00e7al\u0131\u015fmalar\u0131 ilerledik\u00e7e, insan gen haritas\u0131n\u0131 daha net bir \u015fekilde \u00e7izmek m\u00fcmk\u00fcn oldu. \u0130nsan Genomu Projesi\u2019nde, 22 bin gen tan\u0131mlanabilmi\u015fti, ancak toplam gen say\u0131s\u0131n\u0131n yakla\u015f\u0131k 31 bin olmas\u0131 gerekti\u011fi d\u00fc\u015f\u00fcn\u00fcl\u00fcyordu. Celera Genomics ise 26 bin gen ortaya koymu\u015ftu ve muhtemelen 12 bin daha oldu\u011funu ileri s\u00fcr\u00fcyordu. Oysa sonraki d\u00f6nemde ger\u00e7ek gen say\u0131s\u0131n\u0131n \u2018sadece\u2019 20 bin dolay\u0131nda oldu\u011fu anla\u015f\u0131ld\u0131.<\/p>\n

Bu beklenmedik sonu\u00e7, bilim d\u00fcnyas\u0131 i\u00e7in \u015fa\u015f\u0131rt\u0131c\u0131 olmu\u015ftu. \u0130nsandan daha az karma\u015f\u0131k g\u00f6r\u00fcnen ve genomu daha az baz \u00e7iftinden olu\u015fan bir\u00e7ok organizma, orant\u0131l\u0131 olarak \u00e7ok daha fazla gene sahip olabilirdi! \u00d6rne\u011fin maya h\u00fccresi genomu yakla\u015f\u0131k 12,5 milyon baz \u00e7iftinden olu\u015fur ve 5770 protein kodlayan gen bar\u0131nd\u0131r\u0131r. \u00d6te yandan genomu 100 milyon baz \u00e7iftinden olu\u015fan yuvarlak solucan \u201cC. elegans\u201d 20 bin dolay\u0131nda protein kodlayan gene sahiptir. \u0130nsan genomu ise yakla\u015f\u0131k 3,3 milyar baz \u00e7iftinden olu\u015fur ve yukar\u0131da belirtti\u011fimiz \u00fczere 20 bin dolay\u0131nda protein kodlayan gen i\u00e7erir.<\/p>\n

Demek ki insan organizmas\u0131n\u0131n karma\u015f\u0131kl\u0131\u011f\u0131, kromozomlar\u0131ndaki gen say\u0131s\u0131yla do\u011frudan ilintili de\u011fildi. O vakit, sadece insana \u00f6zg\u00fc ve b\u00f6ylece onun karma\u015f\u0131kl\u0131\u011f\u0131n\u0131 a\u00e7\u0131klayabilecek baz\u0131 \u2018\u00f6zel\u2019 genlerin mevcut oldu\u011funu s\u00f6ylemek m\u00fcmk\u00fcn m\u00fcyd\u00fc? Bu sorunun da yan\u0131t\u0131 olumsuzdu: yap\u0131lan ara\u015ft\u0131rmalar, insan genomunun yakla\u015f\u0131k 1300 gen familyas\u0131ndan (\u00f6nemli karakteristikleri payla\u015fan -\u00f6rne\u011fin benzer yap\u0131 ya da i\u015fleve sahip olan aminoasitleri kodlayan- gen gruplar\u0131) olu\u015ftu\u011funu g\u00f6stermi\u015f ve bu familyalar\u0131 sadece insanlarda de\u011fil adeta t\u00fcm canl\u0131lar \u00e2leminde bulmak m\u00fcmk\u00fcn oldu\u011funu ortaya koymu\u015ftu.<\/p>\n

\u00c7\u00f6p DNA<\/strong><\/p>\n

\u0130nsan genomunun sadece protein kodlama genlerinden olu\u015fmad\u0131\u011f\u0131 \u0130nsan Genomu Projesi\u2019nden \u00f6nce biliniyordu. Protein kodlayan genlerin de, tek bir par\u00e7adan olu\u015fmad\u0131\u011f\u0131 anla\u015f\u0131lm\u0131\u015ft\u0131. \u00d6rneklemek gerekirse, g\u00f6z rengi belirleyen bir genin var oldu\u011funu ve bu genin G\u00d6ZRENG\u0130GEN\u0130<\/strong> dizisinden olu\u015ftu\u011funu d\u00fc\u015f\u00fcnelim (bu \u00f6rnekte, kolay anla\u015f\u0131ls\u0131n diye, gen dizisini T\u00fcrk alfabesi harfleriyle yazd\u0131k ama yukar\u0131da da belirtti\u011fimiz gibi DNA, sadece d\u00f6rt harften olu\u015fan -A, C, T ve G- bir alfabe kullan\u0131r). Bu geni, DNA dizisinde, \u00f6rne\u011fin\u00a0 G\u00d6Z<\/strong>AHXTRENB<\/strong>BGTG\u0130<\/strong>UVVTGEN\u0130<\/strong>\u00a0 \u015feklindeki bir k\u00fcme halinde buluruz ve bu k\u00fcmenin (AHXT, BGT, UVVT) ara harfleri (teknik terimle: intronlar) genin bir par\u00e7as\u0131n\u0131 olu\u015fturmazlar. Aminoasit \u00fcretim s\u00fcrecinde, ilk \u00f6nce k\u00fcmenin t\u00fcm\u00fc kopyalan\u0131r fakat daha sonra protein kodlama s\u00fcrecinde bir rol\u00fc olmayan bu ara harfler (intronlar) bir kenara at\u0131l\u0131r.<\/p>\n

Kromozomda \u00e7ok geni\u015f miktarda protein kodlamayan DNA b\u00f6lgelerinin bulundu\u011fu 1960\u2019l\u0131 y\u0131llarda yap\u0131lan \u00e7al\u0131\u015fmalarda \u00f6ng\u00f6r\u00fclm\u00fc\u015ft\u00fc. \u0130nsan genomunun dizilenmesi, bu konuya net bir yan\u0131t getirmeyi sa\u011flad\u0131: DNA dizisinin t\u00fcm\u00fc g\u00f6z \u00f6n\u00fcne al\u0131n\u0131p bu dizinin ne kadar bir k\u0131sm\u0131n\u0131n protein kodlayan genlerden olu\u015ftu\u011fu sorusu soruldu\u011funda, ilgin\u00e7 bir yan\u0131t ile kar\u015f\u0131 kar\u015f\u0131ya kal\u0131nd\u0131: kromozomun ancak \u00e7ok k\u00fc\u00e7\u00fck bir k\u0131sm\u0131 (% 2) protein kodlayan materyalden olu\u015fmakta, arda kalan (% 98\u2019lik) k\u0131sm\u0131 g\u00f6r\u00fcn\u00fcrde herhangi bir i\u015fe yaramamaktayd\u0131. Protein kodlama i\u015flevi olmayan bu DNA dizilerinden, \u2018\u00c7\u00f6p DNA\u2019 (Junk DNA) olarak s\u00f6z edilir.<\/p>\n

Peki, nereden elde etmi\u015ftik genomumuzdaki bu \u00e7\u00f6p DNA\u2019y\u0131? Canl\u0131lar tarihinin kadim zamanlar\u0131nda, insan genomunu olu\u015fturacak olan ilkel h\u00fccrelerin kal\u0131tsal malzemelerine yabanc\u0131 DNA unsurlar\u0131n\u0131n yerle\u015fti\u011fi, sonralar\u0131 bunlar\u0131n \u00e7o\u011fald\u0131\u011f\u0131 ve nihayetinde genomumuzun ayr\u0131lmaz bir par\u00e7as\u0131 haline gelmi\u015f oldu\u011fu d\u00fc\u015f\u00fcn\u00fcl\u00fcyor. \u0130\u015fte genomumuzun yakla\u015f\u0131k % 40\u2019\u0131n\u0131 ve \u00e7\u00f6p DNA\u2019m\u0131z\u0131n \u00f6nemli bir k\u0131sm\u0131n\u0131 bu olay sonucunda elde etti\u011fimiz tahmin ediliyor.<\/p>\n

\"\"
Belki bir i\u015fe yar\u0131yorlard\u0131r!<\/figcaption><\/figure>\n

\u00c7\u00f6p ne i\u015fe yarar?<\/strong><\/p>\n

Peki, \u00e7\u00f6p DNA\u2019n\u0131n, bir evrimsel s\u00fcre\u00e7 sonucu ortaya \u00e7\u0131km\u0131\u015f ve i\u015flevselli\u011fini yitirmi\u015f adeta bir DNA mezarl\u0131\u011f\u0131 oldu\u011funu s\u00f6ylemek m\u00fcmk\u00fcn m\u00fcyd\u00fc? Yoksa onun kromozomlar\u0131m\u0131zda bu denli y\u00fcksek miktarlarda bulunmas\u0131, hen\u00fcz anlamad\u0131\u011f\u0131m\u0131z birtak\u0131m s\u00fcre\u00e7lere mi i\u015faret ediyordu? Hemen belirtelim, konu g\u00fcn\u00fcm\u00fczde h\u00e2l\u00e2 tart\u0131\u015fmal\u0131. Kimilerine g\u00f6re, \u00e7\u00f6p DNA dizileri biyokimyasal etkinlik g\u00f6sterdikleri halde biyolojik fonksiyonlar\u0131n bir par\u00e7as\u0131 de\u011fildir. Di\u011fer u\u00e7ta, (pek \u00e7ok biliminsan\u0131n\u0131n g\u00f6r\u00fc\u015f\u00fcne g\u00f6re sonu\u00e7lar\u0131 epeyce abart\u0131lm\u0131\u015f g\u00f6r\u00fcnen) baz\u0131 \u00e7al\u0131\u015fmalar, insan DNA\u2019s\u0131n\u0131n % 80\u2019e varan bir k\u0131sm\u0131n\u0131n biyolojik s\u00fcre\u00e7lerde rol oynad\u0131\u011f\u0131n\u0131 ileri s\u00fcrm\u00fc\u015ft\u00fcr. \u00c7\u00f6p DNA konusunu ele alan Nessa Carey\u2019in yeni kitab\u0131ndan (1) s\u00f6z etmeden \u00f6nce, \u2018\u00e7\u00f6p\u2019 materyalin varl\u0131\u011f\u0131na anlam vermeye \u00e7al\u0131\u015fan iki farkl\u0131 g\u00f6r\u00fc\u015f a\u00e7\u0131s\u0131n\u0131 k\u0131saca dile getirelim.<\/p>\n

\u2018Yal\u0131t\u0131m teorisi\u2019, biyolojik fonksiyonlar a\u00e7\u0131s\u0131ndan hayati \u00f6nem ta\u015f\u0131yan gen denilen nesneleri kromozomun tek bir b\u00f6lgesinde toplamaktansa onlar\u0131 da\u011f\u0131t\u0131k bir \u015feklide saklaman\u0131n daha etkili oldu\u011funu dolay\u0131s\u0131yla evrimsel a\u00e7\u0131dan tercih edilen bir \u00e7\u00f6z\u00fcm olarak ortaya \u00e7\u0131kt\u0131\u011f\u0131n\u0131 \u00f6ne s\u00fcrm\u00fc\u015ft\u00fcr. B\u00f6ylece \u00e7evreden kaynaklanan sald\u0131r\u0131lar\u0131n (kozmik radyasyonlar, n\u00fckleer emisyonlar, vs.) kromozom yap\u0131 ve i\u015flevi \u00fczerine etkisi \u00f6nemli derecede azalt\u0131lm\u0131\u015f oluyordu.<\/p>\n

\u0130ngiliz biyolog Richard Dawkins ise, bu bilmeceye 1970\u2019li y\u0131llar\u0131n ortas\u0131nda, \u2018bencil genler\u2019 bak\u0131\u015f a\u00e7\u0131s\u0131yla bir yan\u0131t getirdi:<\/p>\n

\u201c\u00d6rne\u011fin, organizmalardaki DNA miktar\u0131n\u0131n, bu organizmalar\u0131 in\u015fa etmek i\u00e7in gereken miktarlar\u0131n \u00f6tesinde oldu\u011fu anla\u015f\u0131lm\u0131\u015ft\u0131r: DNA\u2019n\u0131n geni\u015f bir k\u0131sm\u0131 asla proteine \u00e7evrilmez. (\u2026) Biyologlar, g\u00f6r\u00fcn\u00fcrde fazla olan bu DNA\u2019n\u0131n ne gibi faydal\u0131 g\u00f6revleri olabilece\u011fi konusunda kafa yormaktad\u0131rlar. Bencil genler bak\u0131\u015f a\u00e7\u0131s\u0131ndan bak\u0131ld\u0131\u011f\u0131nda, herhangi bir paradoks yoktur.\u00a0 DNA\u2019n\u0131n ger\u00e7ek \u2018amac\u0131\u2019 sadece hayatta kalmakt\u0131r. Fazla DNA\u2019y\u0131 a\u00e7\u0131klaman\u0131n en basit yolu, onun bir parazit veya en iyi ihtimalle, di\u011fer DNA taraf\u0131ndan yarat\u0131lm\u0131\u015f olan hayatta kalma makinelerinde zarars\u0131z veya l\u00fczumsuz bir otostop yolcusu oldu\u011funu varsaymakt\u0131r.\u201d (2)<\/p>\n

Daha sonralar\u0131, \u00e7\u00f6p DNA\u2019n\u0131n \u00f6nemli bir k\u0131sm\u0131n\u0131n, kendini kopyalayarak tekrar kromozomun i\u00e7ine yerle\u015fme \u00f6zelli\u011fine sahip olan (transpozon olarak bilinen) yap\u0131lardan olu\u015ftu\u011funun anla\u015f\u0131lmas\u0131yla, Dawkins\u2019in g\u00f6r\u00fc\u015f\u00fcn\u00fcn daha da anlam kazanm\u0131\u015f oldu\u011fu d\u00fc\u015f\u00fcn\u00fclebilir.<\/p>\n

\"\"Nessa Carey\u2019nin kitab\u0131<\/strong><\/p>\n

\u201c\u00c7\u00f6p DNA\u201d (1) adl\u0131 son kitab\u0131nda, Nessa Carey bu ilgin\u00e7 konuyu ayr\u0131nt\u0131l\u0131 olarak ele al\u0131yor ve genomumuzun h\u00e2l\u00e2 karanl\u0131k g\u00f6r\u00fcnen bu k\u0131sm\u0131na \u0131\u015f\u0131k tutmaya \u00e7al\u0131\u015f\u0131yor.<\/p>\n

Yukar\u0131da maya h\u00fccresi ve yuvarlak solucan \u00f6rneklerini verirken, gen say\u0131s\u0131n\u0131n, bir organizman\u0131n karma\u015f\u0131kl\u0131\u011f\u0131n\u0131n g\u00f6stergesi olmayabilece\u011finin alt\u0131n\u0131 \u00e7izdik. Fakat buna kar\u015f\u0131n, Carey\u2019in yans\u0131tt\u0131\u011f\u0131 g\u00f6r\u00fc\u015fe g\u00f6re, karma\u015f\u0131kl\u0131\u011f\u0131n, daha ziyade protein kodlamayan DNA miktar\u0131yla ba\u011f\u0131nt\u0131l\u0131 oldu\u011fu d\u00fc\u015f\u00fcn\u00fclebilir: daha karma\u015f\u0131k organizmalar\u0131n daha fazla \u00e7\u00f6p DNA\u2019ya sahip olduklar\u0131 g\u00f6r\u00fcnmektedir (\u00f6rne\u011fin bakteriler, maya, yuvarlak solucan, meyve sine\u011fi, fare ve insan kar\u015f\u0131la\u015ft\u0131r\u0131ld\u0131\u011f\u0131nda b\u00f6yle bir tabloyu ortaya koymak m\u00fcmk\u00fcn).\u00a0 \u0130nsan, meyve sine\u011fi ve yuvarlak solucan gen say\u0131s\u0131 birbirinden \u00e7ok farkl\u0131 de\u011fil, ama insandaki \u00e7\u00f6p DNA bu organizmalara k\u0131yasla \u00e7ok daha fazla.<\/p>\n

Nessa Carey kitab\u0131nda, \u00e7\u00f6p DNA\u2019n\u0131n ger\u00e7i do\u011frudan protein kodlama gibi bir i\u015flevi olamad\u0131\u011f\u0131n\u0131, ancak protein kodlayan genlerimizi etkileyip, bir\u00e7ok hastal\u0131klar\u0131n ortaya \u00e7\u0131k\u0131\u015f\u0131nda rol oynad\u0131\u011f\u0131n\u0131 ve h\u00fccre i\u00e7i s\u00fcre\u00e7ler \u00fczerine son derece \u00f6nemli etkileri oldu\u011funu son y\u0131llar\u0131n ara\u015ft\u0131rmalar\u0131n\u0131 yans\u0131tarak a\u00e7\u0131kl\u0131yor.<\/p>\n

\u00d6rne\u011fin \u00e7\u00f6p DNA\u2019n\u0131n bir par\u00e7as\u0131 olarak g\u00f6rebilece\u011fimiz intronlar\u0131n, baz\u0131 hastal\u0131klar\u0131n (Friedreich ataksisi hastal\u0131\u011f\u0131nda oldu\u011fu gibi) ortaya \u00e7\u0131k\u0131\u015f\u0131nda \u00e7ok \u00f6nemli bir rol oynad\u0131\u011f\u0131 anla\u015f\u0131l\u0131yor.<\/p>\n

\"\"
Nessa Carey<\/figcaption><\/figure>\n

\u00c7\u00f6p DNA\u2019n\u0131n \u00f6nemli bir k\u0131sm\u0131, \u201cserpi\u015ftirilmi\u015f tekrarlar\u201d denilen baz\u0131 spesifik DNA dizilerinin tekrarlanmas\u0131ndan olu\u015fuyor. DNA\u2019daki bu tekrarlama b\u00f6lgelerinin, birtak\u0131m h\u00fccre i\u00e7i s\u00fcre\u00e7lerde son derece \u00f6nemli bir rol oynad\u0131\u011f\u0131 belirlenmi\u015f bulunuyor. \u00d6rne\u011fin tekrarlama b\u00f6lgelerinin, h\u00fccre b\u00f6l\u00fcnmesindeki \u201ckrossing over\u201d denilen olay (kromozomlar aras\u0131ndaki par\u00e7a de\u011fi\u015fimi) \u00fczerine etki edebilece\u011fi ve bunun sonucu olarak kromozomda fazladan DNA dizilerinin olu\u015fabilece\u011fi ya da bulunmas\u0131 gereken baz\u0131 dizilerin de hi\u00e7 olu\u015famayaca\u011f\u0131 ve bu t\u00fcrden anomaliler sonucu, Carcot-Marie-Tooth hastal\u0131\u011f\u0131 ya da Williams-Beuren sendromu gibi, baz\u0131 kal\u0131tsal hastal\u0131klar\u0131n ba\u015f g\u00f6sterebilece\u011fi g\u00f6zlemlenmi\u015ftir.<\/p>\n

\u0130lgin\u00e7 olan, sadece uzun (100 baz \u00e7ifti ya da fazlas\u0131) de\u011fil, insan genomunun yakla\u015f\u0131k % 3\u2019\u00fcn\u00fc olu\u015fturan k\u0131sa tekrarlar da sorun yaratabilir. Bu tipten tekrarlardaki aksamalar \u00f6rne\u011fin Frajil X sendromu, Friedreich\u2019s ataksisi veya mytonik distrofi gibi kal\u0131tsal genetik hastal\u0131klar\u0131n temelinde yatar. T\u00fcm bu hastal\u0131klarda, \u00e7\u00f6p DNA\u2019daki sadece 3 baz \u00e7iftinden olu\u015fan tekrarlar\u0131n gere\u011finden fazla tekrarlan\u0131\u015f\u0131 hastal\u0131\u011fa yol a\u00e7ar.<\/p>\n

Nessa Carey\u2019nin verdi\u011fi pek \u00e7ok \u00f6rnekten son olarak telomerlere de\u011finelim. TTAGGG alt\u0131l\u0131 baz-\u00e7iftlerinin tekrarlan\u0131\u015f\u0131ndan meydana gelen telomerler, kromozomlar\u0131n u\u00e7lar\u0131n\u0131 olu\u015fturur (ayakkab\u0131 ba\u011fc\u0131\u011f\u0131n\u0131n ucundaki, ba\u011fc\u0131\u011f\u0131n \u00e7\u00f6z\u00fclmesini \u00f6nleyen plastik par\u00e7alara benzetebiliriz). Yeni do\u011fan bebekte TTAGGG motifi yakla\u015f\u0131k 10 bin baz-\u00e7ifti uzunlu\u011funda olur ve organizma ya\u015fland\u0131k\u00e7a (h\u00fccreler b\u00f6l\u00fcnd\u00fck\u00e7e), bu uzunluk azal\u0131r. Ger\u00e7ekte telomer denilen yap\u0131, \u00e7\u00f6p DNA\u2019dan (ve protein komplekslerinden) olu\u015fur. Telomerlerin in\u015fas\u0131, h\u00fccre taraf\u0131ndan \u00fcretilen bir RNA molek\u00fcl\u00fcne ba\u011fl\u0131d\u0131r; ancak ilgin\u00e7tir ki bu RNA, protein kodlamada de\u011fil telomerin olu\u015fturulmas\u0131nda yer al\u0131r. V\u00fccudun ya\u015flanma s\u00fcreciyle yak\u0131ndan ilintili olan telomerler e\u011fer sa\u011fl\u0131kl\u0131 bir \u015fekilde olu\u015fturulamam\u0131\u015fsa, birtak\u0131m hastal\u0131klar ortaya \u00e7\u0131kabilir (insan telomer sendromu gibi).<\/p>\n

Sonu\u00e7 olarak \u00e7\u00f6p DNA\u2019n\u0131n, at\u0131l ve etkisiz DNA dizilerinden olu\u015fmad\u0131\u011f\u0131 anla\u015f\u0131l\u0131yor. Onlardan art\u0131k gitgide \u00e7\u00f6p DNA de\u011fil de \u2018kodlamayan DNA\u2019 (noncoding DNA) \u015feklinde s\u00f6z edilmesi, bu anlay\u0131\u015f\u0131n yayg\u0131nla\u015ft\u0131\u011f\u0131n\u0131 g\u00f6stermektedir \u015f\u00fcphesiz. Kromozomlar\u0131m\u0131z\u0131n bu \u2018karanl\u0131k madde\u2019sinin ara\u015ft\u0131rmac\u0131lar\u0131 daha uzun y\u0131llar me\u015fgul edece\u011fi \u015f\u00fcphesiz. Hi\u00e7 beklenmedik sonu\u00e7lara haz\u0131r olal\u0131m!<\/p>\n

Dipnotlar<\/strong><\/p>\n

1) Nessa Carey, Junk DNA \u2013 A Journey Trough the Dark Matter of the Genome<\/em>, Icon Book Ltd., London, 2015.
\n2) Richard Dawkins, The Selfish Gene<\/em>, Oxford University Press, 1976.<\/p>\n

 <\/p>\n","protected":false},"excerpt":{"rendered":"

\u00c7\u00f6p DNA\u2019n\u0131n, at\u0131l ve etkisiz DNA dizilerinden olu\u015fmad\u0131\u011f\u0131 anla\u015f\u0131l\u0131yor. Onlardan art\u0131k \u00e7\u00f6p DNA de\u011fil de \u2018kodlamayan DNA\u2019 (noncoding DNA) \u015feklinde s\u00f6z edilmesi, bu anlay\u0131\u015f\u0131n yayg\u0131nla\u015ft\u0131\u011f\u0131n\u0131 g\u00f6steriyor. Kromozomlar\u0131m\u0131z\u0131n bu \u2018karanl\u0131k madde\u2019sinin ara\u015ft\u0131rmac\u0131lar\u0131 daha uzun y\u0131llar me\u015fgul edece\u011fi \u015f\u00fcphesiz. Hi\u00e7 beklenmedik sonu\u00e7lara haz\u0131r olal\u0131m! 2000\u2019li y\u0131llar\u0131n ba\u015flar\u0131nda, insan genomunun dizilenmesi, insan akl\u0131n\u0131n ve bilimin en b\u00fcy\u00fck zaferlerinden […]<\/p>\n","protected":false},"author":508,"featured_media":16298,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[181,21,1473,231],"tags":[272,431,292,525],"class_list":["post-16297","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-144-sayi","category-biyoloji","category-genis-aci","category-molekuler-biyoloji-ve-genetik","tag-dna","tag-gen","tag-genetik","tag-kromozom"],"acf":[],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/posts\/16297","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/users\/508"}],"replies":[{"embeddable":true,"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/comments?post=16297"}],"version-history":[{"count":0,"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/posts\/16297\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/media\/16298"}],"wp:attachment":[{"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/media?parent=16297"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/categories?post=16297"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/tags?post=16297"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}