{"id":23435,"date":"2015-03-01T13:11:58","date_gmt":"2015-03-01T11:11:58","guid":{"rendered":"https:\/\/bilimvegelecek.com.tr\/?p=23435"},"modified":"2018-04-17T13:22:01","modified_gmt":"2018-04-17T10:22:01","slug":"dunyada-yasamin-baslangici","status":"publish","type":"post","link":"https:\/\/bilimvegelecek.com.tr\/index.php\/2015\/03\/01\/dunyada-yasamin-baslangici","title":{"rendered":"D\u00fcnyada ya\u015fam\u0131n ba\u015flang\u0131c\u0131"},"content":{"rendered":"

Ya\u015fam i\u00e7in gereken yap\u0131ta\u015flar\u0131n\u0131n d\u00fcnya \u00fczerindeki s\u00fcre\u00e7ler sonucunda olu\u015fmas\u0131 m\u00fcmk\u00fcn oldu\u011fu gibi, uzaydan ta\u015f\u0131nmas\u0131 da m\u00fcmk\u00fcn g\u00f6r\u00fcn\u00fcyor. D\u00fcnyada ya\u015fam\u0131n ilk bi\u00e7imi, do\u011fal olarak bug\u00fcn\u00fcn en basit ya\u015fam bi\u00e7imlerinden daha basit, minimum say\u0131da fonksiyonel birim \u00fczerine kurulmu\u015f olmal\u0131d\u0131r. Ya\u015fam\u0131n ba\u015flang\u0131c\u0131 i\u00e7in hen\u00fcz bir standart model yoktur, ancak baz\u0131 hipotezler bilim d\u00fcnyas\u0131nda ilgi g\u00f6rmektedir.<\/em><\/p>\n

Ya\u015fam\u0131n k\u00f6keni, biyolojik evrimle kar\u015f\u0131la\u015ft\u0131r\u0131ld\u0131\u011f\u0131nda \u00e7ok daha zorlu bir soru olarak g\u00f6z\u00fckmektedir. Bunun en temel nedeni, biyolojik evrim arkas\u0131nda, aralar\u0131nda fosillerin de bulundu\u011fu pek \u00e7ok somut iz b\u0131rak\u0131rken, ya\u015fam\u0131n ba\u015flang\u0131c\u0131na ili\u015fkin benzer izler ve ipu\u00e7lar\u0131n\u0131n bulunmamas\u0131d\u0131r. D\u00fcnyada var olmu\u015f t\u00fcm canl\u0131lar\u0131n y\u00fczde 99 kadar\u0131n\u0131n soyu t\u00fckenmi\u015f olsa da, bug\u00fcn d\u00fcnyada var oldu\u011fu tahmin edilen toplam 10-14 milyon t\u00fcr canl\u0131n\u0131n tamam\u0131n\u0131n bir ortak atadan farkl\u0131la\u015ft\u0131\u011f\u0131 konusunda bilim d\u00fcnyas\u0131 hemfikirdir. Bu son evrensel ortak atan\u0131n (LUCA: Last Universal Common Ancestor) ise nas\u0131l ortaya \u00e7\u0131kt\u0131\u011f\u0131 konusunda farkl\u0131 hipotezler vard\u0131r.<\/p>\n

Somut kan\u0131tlarla desteklenen bilgiler \u015f\u00f6yle \u00f6zetlenebilir:<\/strong><\/p>\n

D\u00fcnya 4,5 milyar y\u0131l ya\u015f\u0131ndad\u0131r. Ya\u015fam bi\u00e7imlerine ait en erken mikrobiyel fosiller 3,5 milyar y\u0131l \u00f6ncesinden kalm\u0131\u015ft\u0131r. Biyojenik, yani canl\u0131lar\u0131n etkinlikleri sonucunda olu\u015fabilecek kimyasallar\u0131n izleri ise en erken 3,7 milyar y\u0131ll\u0131k tortul kaya\u00e7larda g\u00f6r\u00fclm\u00fc\u015ft\u00fcr. 4,1 milyar y\u0131l \u00f6ncesinden 3,8 milyar y\u0131l \u00f6ncesine kadar \u00f6zellikle g\u00fcne\u015f sisteminin gazdan olu\u015fan d\u0131\u015f gezegenlerinin y\u00f6r\u00fcngelerindeki hareketlilik nedeniyle, \u00e7ok b\u00fcy\u00fck s\u0131kl\u0131kta, b\u00fcy\u00fck k\u00fctleli cisimlerle \u00e7arp\u0131\u015fmalar olmu\u015ftur. Bu \u201ca\u011f\u0131r bombard\u0131man\u201d d\u00f6neminin biti\u015finden sonra ya\u015fam\u0131n ortaya \u201ck\u0131sa\u201d bir s\u00fcre i\u00e7inde \u00e7\u0131kt\u0131\u011f\u0131 anla\u015f\u0131lmaktad\u0131r. \u00d6te yandan d\u00fcnyan\u0131n 4 milyar y\u0131l \u00f6nceki atmosferik bile\u015fimine enerji aktar\u0131m\u0131 ile yap\u0131lan me\u015fhur Miller deneyleri (sonras\u0131nda farkl\u0131 ko\u015fullarda bu deneyler tekrarlanm\u0131\u015ft\u0131r) ile ya\u015fam\u0131n yap\u0131ta\u015flar\u0131, \u00f6rne\u011fin, aminoasitler, karbohidratlar, n\u00fckleik asit bile\u015fenlerinin olu\u015fabildi\u011fi g\u00f6sterilmi\u015ftir.<\/p>\n

Bunun d\u0131\u015f\u0131nda, d\u00fcnyaya \u00e7arpan meteorlarda, kuyruklu y\u0131ld\u0131zlarda, Sat\u00fcrn ve J\u00fcpiter\u2019in baz\u0131 uydular\u0131nda ya\u015fam i\u00e7in \u00f6nemli molek\u00fcllerin izlerine rastlanm\u0131\u015ft\u0131r.<\/p>\n

Sonu\u00e7 olarak, ya\u015fam i\u00e7in gereken yap\u0131ta\u015flar\u0131n\u0131n d\u00fcnya \u00fczerindeki s\u00fcre\u00e7ler sonucunda olu\u015fmas\u0131 m\u00fcmk\u00fcn oldu\u011fu gibi, uzaydan ta\u015f\u0131nmas\u0131 da m\u00fcmk\u00fcn g\u00f6r\u00fcnmektedir. D\u00fcnyada ya\u015fam\u0131n ilk bi\u00e7imi, do\u011fal olarak bug\u00fcn\u00fcn en basit ya\u015fam bi\u00e7imlerinden daha basit, minimum say\u0131da fonksiyonel birim \u00fczerine kurulmu\u015f olmal\u0131d\u0131r. Ya\u015fam\u0131n ba\u015flang\u0131c\u0131 i\u00e7in hen\u00fcz bir standart model yoktur, ancak \u015fu hipotezler bilim d\u00fcnyas\u0131nda ilgi g\u00f6rmektedir.<\/p>\n

\u00d6nce replikasyon<\/strong><\/p>\n

Ya\u015fam\u0131n en karakteristik \u00f6zelliklerinden biri, kendinin kopyalar\u0131n\u0131 olu\u015fturabilmesidir. Molek\u00fcler d\u00fczeyde bu kendini kopyalayabilen bile\u015fikler arac\u0131l\u0131\u011f\u0131yla ger\u00e7ekle\u015ftirilebilir. Bu bile\u015fiklerin protein sentezini kodlamas\u0131 daha sonra kazan\u0131lan bir karakter olabilir. Otokataliz, yani kendinin sentezini kataliz edebilme \u00f6zelli\u011finin kimyasal \u00f6rnekleri bilinmektedir. Bu bilgi ta\u015f\u0131yacak molek\u00fcl\u00fcn temel \u00f6zellikleridir.<\/p>\n

\"\"
\u0130lksel d\u00fcnya ko\u015fullar\u0131n\u0131 g\u00f6steren temsili bir resim.<\/figcaption><\/figure>\n

\u00d6nce metabolizma<\/strong><\/p>\n

Canl\u0131l\u0131\u011f\u0131n temel fonksiyonlar\u0131n\u0131n ger\u00e7ekle\u015fmesi i\u00e7in birbiriyle ba\u011flant\u0131l\u0131 bir reaksiyon serisinin s\u00fcrd\u00fcr\u00fclebilmesi gerekir. \u0130lksel d\u00fcnya ko\u015fullar\u0131ndaki denizlerde, metabolik reaksiyonlar\u0131n olu\u015fabilece\u011fi laboratuvarda g\u00f6sterilmi\u015ftir. \u00d6zellikle bir enerji kayna\u011f\u0131n\u0131n yak\u0131n\u0131nda bu gibi metabolizma benzeri reaksiyonlar serisinin s\u00fcrd\u00fcr\u00fclmesi m\u00fcmk\u00fcn g\u00f6r\u00fclmektedir. Su alt\u0131 bacalar\u0131, okyanuslar\u0131n taban\u0131nda hem enerji hem de kimyasal olarak reaktif bile\u015fikler sa\u011flayarak bu gibi s\u00fcre\u00e7lerin ortaya \u00e7\u0131kmas\u0131n\u0131 sa\u011flayabilir. Wachtershauser taraf\u0131ndan \u00f6nerilen olas\u0131l\u0131k ise, demir-s\u00fclf\u00fcr d\u00fcnyas\u0131 hipotezidir. Demir-s\u00fclf\u00fcr d\u00fcnyas\u0131nda atmosferik gaz bile\u015fenler demir-s\u00fclf\u00fcr y\u00fczeylerinde daha kompleks yap\u0131lara d\u00f6n\u00fc\u015ft\u00fcr\u00fcl\u00fcrler, \u00f6rne\u011fin karbondioksitin biyosentetik kullan\u0131m\u0131 bu tip ilk metabolik reaksiyonlara \u00f6rnek olarak g\u00f6sterilir.<\/p>\n

RNA d\u00fcnyas\u0131<\/strong><\/p>\n

Bug\u00fcn bildi\u011fimiz bi\u00e7imiyle ya\u015fam iki \u00f6nemli bile\u015fenden olu\u015fmaktad\u0131r. Genetik ve metabolizma. Genetik karakter esas olarak kendini kopyalayabilen biyomolek\u00fcllere (n\u00fckleik asit) ihtiya\u00e7 duyarken, metabolizma ise reaksiyonlar\u0131 h\u0131zland\u0131racak kataliz\u00f6rlere (enzim, proteinler) ihtiya\u00e7 duyacakt\u0131r. Dolay\u0131s\u0131yla bug\u00fcn bu iki i\u015flev birbirinden \u00e7ok farkl\u0131 molek\u00fcller arac\u0131l\u0131\u011f\u0131yla ger\u00e7ekle\u015ftirilmektedir. Ancak, 1989 y\u0131l\u0131nda kimya alan\u0131nda Nobel \u00f6d\u00fcl\u00fc alan Sidney Altman ve Thomas Cech, RNA\u2019n\u0131n genetik bilginin aktar\u0131lmas\u0131, kopyalanmas\u0131, ta\u015f\u0131nmas\u0131na ek olarak, kataliz\u00f6r rol\u00fc oldu\u011funu da g\u00f6stermi\u015flerdir. Bu durumda bu iki kritik g\u00f6revi de \u00fcstlenebilecek tek bir molek\u00fcl varsa, o zaman belki de ya\u015fam\u0131n ilk formu RNA \u00fczerine kurulu olabilirdi.\u00a0 Bu d\u00fc\u015f\u00fcnceyi destekleyen pek \u00e7ok ek bulgu olmas\u0131na ra\u011fmen, kimyasal bak\u0131mdan RNA\u2019n\u0131n da olduk\u00e7a kompleks bir bile\u015fik olmas\u0131 sorunun nihai yan\u0131t\u0131n\u0131n bu olmayaca\u011f\u0131n\u0131 d\u00fc\u015f\u00fcnd\u00fcrm\u00fc\u015ft\u00fcr.<\/p>\n

Panspermi\/ekzojenez<\/strong><\/p>\n

Panspermi d\u00fc\u015f\u00fcncesi, evrende ya\u015fam\u0131n metoridler, asteroidler, kuyrukluy\u0131ld\u0131zlar, gezegensiler ve hatta bilin\u00e7li olmasa da uzay ara\u00e7lar\u0131 ile ta\u015f\u0131nd\u0131\u011f\u0131n\u0131 savunmaktad\u0131r. Bu hipotezi destekleyen bulgular aras\u0131nda ekstremofiller gibi baz\u0131 organizmalar\u0131n uzay bo\u015flu\u011fundaki ko\u015fullara dayanabilecek olmas\u0131 vard\u0131r. Bu hipotez ger\u00e7ekte ilk ya\u015fam\u0131n nas\u0131l olu\u015ftu\u011funu de\u011fil, ancak evrende ya\u015fam\u0131n nas\u0131l yay\u0131labilece\u011fini a\u00e7\u0131klamaktad\u0131r. Ya\u015fam\u0131n temel yap\u0131 ta\u015flar\u0131n\u0131n uzayda \u00e7e\u015fitli yerlerde bulunmas\u0131 bu hipotezi k\u0131smen destekleyebilir, \u00f6te yandan bu bile\u015fiklerin d\u00fcnyaya ya\u015fam\u0131n bile\u015fenleri olarak ta\u015f\u0131nmas\u0131 daha olas\u0131 olarak g\u00f6r\u00fclmektedir.<\/p>\n

\"\"
Su alt\u0131 bacalar\u0131, okyanuslar\u0131n taban\u0131nda hem enerji hem de kimyasal olarak reaktif bile\u015fikler sa\u011flayarak metabolik reaksiyonlar\u0131n ortaya \u00e7\u0131kmas\u0131n\u0131 sa\u011flayabilir. (Atlas Okyanusunun taban\u0131nda bir su alt\u0131 bacas\u0131)<\/figcaption><\/figure>\n

Lipid d\u00fcnyas\u0131<\/strong><\/p>\n

Bu hipoteze g\u00f6re kendini kopyalayan ilk yap\u0131 lipid benzeri bir yap\u0131yd\u0131. Fosfolipidlerin, su i\u00e7inde t\u0131pk\u0131 h\u00fccre zar\u0131 yap\u0131s\u0131nda oldu\u011fu gibi, \u00e7ift-katmanl\u0131 lipid yap\u0131lar olu\u015fturdu\u011fu bilinmektedir. Yeni lipid bile\u015fenlerin kat\u0131l\u0131m\u0131yla bu yap\u0131lar geni\u015fleyebilmekte ve hatta a\u015f\u0131r\u0131 geni\u015fleme b\u00f6l\u00fcnmeyi tetikleyerek, ayn\u0131 lipid bile\u015fenlerinden olu\u015fan iki yavru olu\u015fturabilmektedir. \u0130lksel d\u00fcnya ko\u015fullar\u0131nda, \u00e7ok farkl\u0131 yap\u0131larda potansiyel lipid t\u00fcrevleri varken sadece ayn\u0131 karakterde \u00e7ift-katmal\u0131 lipid toplar\u0131n\u0131n \u00e7o\u011falmas\u0131 bir t\u00fcr kimyasal se\u00e7ilimi ortaya \u00e7\u0131karm\u0131\u015f olabilir. \u0130lk metabolik reaksiyonlar\u0131n, nano-\u00f6l\u00e7ekte bir deney t\u00fcp\u00fc olarak da g\u00f6r\u00fclebilecek bir \u00e7ift-katmanl\u0131 lipid top i\u00e7inde ortaya \u00e7\u0131k\u0131p geli\u015fmesi de \u00e7ok makul g\u00f6z\u00fckmektedir.<\/p>\n

Farkl\u0131 hipotezlerden anla\u015f\u0131laca\u011f\u0131 gibi, ya\u015fam\u0131n ba\u015flang\u0131c\u0131, bir ara\u015ft\u0131rma alan\u0131 olarak \u00e7ok caziptir. Ger\u00e7ekte ya\u015fam, birden fazla farkl\u0131 bi\u00e7imde ortaya \u00e7\u0131km\u0131\u015f olabilir. Ve sonu\u00e7 olarak, biz d\u00fcnyada bunlardan hangisi \u00fczerinden ya\u015fam\u0131n ortaya \u00e7\u0131kt\u0131\u011f\u0131n\u0131 bilemeyebiliriz. Ancak, laboratuvar ko\u015fullar\u0131 alt\u0131nda bu yakla\u015f\u0131mlar\u0131n herhangi biriyle, ya\u015fam\u0131n karakteristik niteliklerine ula\u015fmak heyecan verici olacakt\u0131r. Bu niteliklerin ne oldu\u011fu konusunda tart\u0131\u015fma olsa da, ya\u015fam\u0131n en basit bi\u00e7imiyle kimyasal s\u00fcre\u00e7ler sonucunda ortaya \u00e7\u0131kabilece\u011fi konusunda ku\u015fku yoktur.<\/p>\n","protected":false},"excerpt":{"rendered":"

Ya\u015fam i\u00e7in gereken yap\u0131ta\u015flar\u0131n\u0131n d\u00fcnya \u00fczerindeki s\u00fcre\u00e7ler sonucunda olu\u015fmas\u0131 m\u00fcmk\u00fcn oldu\u011fu gibi, uzaydan ta\u015f\u0131nmas\u0131 da m\u00fcmk\u00fcn g\u00f6r\u00fcn\u00fcyor. D\u00fcnyada ya\u015fam\u0131n ilk bi\u00e7imi, do\u011fal olarak bug\u00fcn\u00fcn en basit ya\u015fam bi\u00e7imlerinden daha basit, minimum say\u0131da fonksiyonel birim \u00fczerine kurulmu\u015f olmal\u0131d\u0131r. Ya\u015fam\u0131n ba\u015flang\u0131c\u0131 i\u00e7in hen\u00fcz bir standart model yoktur, ancak baz\u0131 hipotezler bilim d\u00fcnyas\u0131nda ilgi g\u00f6rmektedir. Ya\u015fam\u0131n k\u00f6keni, biyolojik […]<\/p>\n","protected":false},"author":389,"featured_media":23440,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[170,21,32],"tags":[197,2873,595,2874,2872],"class_list":["post-23435","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-133-sayi","category-biyoloji","category-evrim","tag-biyoloji","tag-dunyada-yasam","tag-yasam","tag-yasamin-baslangici","tag-yasamin-tarihi"],"acf":[],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/posts\/23435","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\/389"}],"replies":[{"embeddable":true,"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/comments?post=23435"}],"version-history":[{"count":0,"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/posts\/23435\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/media\/23440"}],"wp:attachment":[{"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/media?parent=23435"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/categories?post=23435"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/tags?post=23435"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}