{"id":39621,"date":"2020-01-09T03:17:52","date_gmt":"2020-01-09T00:17:52","guid":{"rendered":"https:\/\/bilimvegelecek.com.tr\/?p=39621"},"modified":"2020-01-08T11:24:17","modified_gmt":"2020-01-08T08:24:17","slug":"yasam-icin-gerekli-oncu-molekuller-nelerdir-ilksel-corba-kurami-ne-soylemektedir","status":"publish","type":"post","link":"https:\/\/bilimvegelecek.com.tr\/index.php\/2020\/01\/09\/yasam-icin-gerekli-oncu-molekuller-nelerdir-ilksel-corba-kurami-ne-soylemektedir","title":{"rendered":"Ya\u015fam i\u00e7in gerekli \u00f6nc\u00fc molek\u00fcller nelerdir? \u0130lksel \u00e7orba kuram\u0131 ne s\u00f6ylemektedir?"},"content":{"rendered":"

D\u00fcnya \u00fczerinde ilk canl\u0131 organizma birdenbire ortaya \u00e7\u0131kmad\u0131. H\u00fccre olu\u015fmadan \u00f6nce bir\u00e7ok \u00f6nc\u00fc ad\u0131m\u0131n ge\u00e7il mesi gerekti. D\u00fcnya\u2019n\u0131n yakla\u015f\u0131k 4,5 milyar y\u0131l \u00f6nce olu\u015ftu\u011fundan ve canl\u0131l\u0131\u011f\u0131n da yakla\u015f\u0131k 3,5-3,8 milyar y\u0131l \u00f6nce ortaya \u00e7\u0131km\u0131\u015f olmas\u0131 gerekti\u011finden bahsetmi\u015ftik. G\u00f6r\u00fcl\u00fcyor ki, D\u00fcnya olu\u015ftuktan sonra ge\u00e7en 700 milyon-1 milyar y\u0131l kadar s\u00fcre, canl\u0131l\u0131\u011f\u0131n olu\u015fmas\u0131 i\u00e7in gerekli uygun ko\u015fullar\u0131n meydana gelmesini sa\u011flad\u0131.<\/p>\n

Do\u011fa bilimlerinde d\u00fcnya \u00fczerindeki ya\u015fam\u0131n cans\u0131z maddelerden nas\u0131l olu\u015ftu\u011funu anlamaya \u00e7al\u0131\u015fan alana \u201ckimyasal evrim\u201d ya da \u201cabiogenesis\u201d ad\u0131 verilir. Abiogenesisin evrim kuram\u0131 ile kar\u0131\u015ft\u0131r\u0131lmamas\u0131 gerekir. Evrim kuram\u0131 temel anlamda canl\u0131lar\u0131n zaman i\u00e7inde nas\u0131l de\u011fi\u015fti\u011fini ve \u00e7e\u015fitlendi\u011fini anlat\u0131rken, abiogenesis cans\u0131z maddelerden canl\u0131 organizmalara ge\u00e7i\u015fin nas\u0131l oldu\u011funu a\u00e7\u0131klamaya \u00e7al\u0131\u015f\u0131r.
\nT\u00fcm canl\u0131 organizmalar h\u00fccrelerden olu\u015fmu\u015ftur. H\u00fccreler, cans\u0131z molek\u00fcllerden birdenbire olu\u015famayacak kadar karma\u015f\u0131k birimlerdir. D\u00fcnya \u00fczerinde canl\u0131l\u0131k ortaya \u00e7\u0131karken de do\u011frudan h\u00fccre yap\u0131s\u0131 de\u011fil, baz\u0131 ara basamaklar olu\u015fmu\u015f olmal\u0131d\u0131r. \u00d6rne\u011fin h\u00fccre yap\u0131s\u0131n\u0131n temel ta\u015flar\u0131 olan proteinler ya da n\u00fckleik asitler de (DNA ve RNA) karma\u015f\u0131k yap\u0131dad\u0131r ve h\u00fccre olu\u015fmadan \u00f6nce bu gibi karma\u015f\u0131k yap\u0131lar\u0131n olu\u015fmu\u015f olmas\u0131 gerekir. Bilim insanlar\u0131 \u00f6ne s\u00fcrd\u00fckleri farkl\u0131 hipotezlerle h\u00fccrenin olu\u015fumuna kadar giden ara basamaklar\u0131 anlamaya ve bu basamaklarda etkili olan kilit molek\u00fclleri ortaya \u00e7\u0131karmaya \u00e7al\u0131\u015f\u0131yor. \u00d6ne s\u00fcr\u00fclen hipotezlerin hi\u00e7birine kesin olarak do\u011fru diyemesek de, s\u00fcrekli elde edilen yeni kan\u0131tlar baz\u0131 hipotezleri di\u011ferlerinden \u00f6ne \u00e7\u0131kar\u0131yor. Bilim d\u00fcnyas\u0131nda kabul g\u00f6ren ve canl\u0131l\u0131\u011f\u0131n nas\u0131l ortaya \u00e7\u0131kt\u0131\u011f\u0131n\u0131 anlatan ara basamaklar\u0131 k\u0131saca \u015f\u00f6yle \u00f6zetleyebiliriz:<\/p>\n

Birinci ad\u0131m: <\/strong>\u00d6ncelikle, ya\u015fam\u0131n ortaya \u00e7\u0131kabilmesi i\u00e7in gerekli \u00e7evresel ortam olu\u015fmu\u015f olmal\u0131d\u0131r. Bu y\u00fczden ilk ad\u0131m olarak D\u00fcnya\u2019n\u0131n ve atmosferin olu\u015fmas\u0131 d\u00fc\u015f\u00fcn\u00fclebilir. Bu a\u015fama ya\u015fam\u0131n olu\u015fmas\u0131 i\u00e7in gerekli inorganik hammaddelerin ortaya \u00e7\u0131kt\u0131\u011f\u0131 ve birbirleriyle etkile\u015fime ge\u00e7ti\u011fi a\u015famad\u0131r. Uygun \u00e7evre ko\u015fullar\u0131n\u0131n olu\u015fmas\u0131 baz\u0131 gezegenleri di\u011ferlerinden farkl\u0131 yapacakt\u0131r.<\/p>\n

\u0130kinci ad\u0131m: <\/strong>\u0130norganik molek\u00fcllerin birbiriyle etkile\u015fimleri sonucu organik molek\u00fcller olu\u015fmaya ba\u015flam\u0131\u015ft\u0131r. Bu reaksiyonlar i\u00e7in gerekli olan enerji de y\u0131ld\u0131r\u0131mlar, g\u00fcne\u015f \u0131\u015f\u0131\u011f\u0131ndan gelen mor \u00f6tesi radyasyon ya da volkanlardan gelen \u0131s\u0131 enerjisinden elde edilmi\u015ftir. Ya\u015fam\u0131n olu\u015fmas\u0131nda rol oynam\u0131\u015f organik molek\u00fcller iki farkl\u0131 kayna\u011fa sahip olabilir: Organik molek\u00fcller d\u00fcnya \u00fczerinde olu\u015fmu\u015f olabilir. Bunun i\u00e7in D\u00fcnya atmosferindeki enerji kaynaklar\u0131ndan yararlan\u0131lm\u0131\u015f olabilir.<\/p>\n

Organik molek\u00fcller D\u00fcnya\u2019da olu\u015fmak yerine uzaydan D\u00fcnya\u2019ya gelmi\u015f olabilir. D\u00fcnya\u2019ya \u00e7arpan g\u00f6kcisimleriyle (kondritler-ta\u015fs\u0131 meteoritler) ta\u015f\u0131nm\u0131\u015f ya da D\u00fcnya\u2019n\u0131n \u00e7ekim kuvveti ile \u00e7ekilmi\u015f de olabilirler.<\/p>\n

\u00dc\u00e7\u00fcnc\u00fc ad\u0131m: <\/strong>D\u00fcnya\u2019da olu\u015fan ya da D\u00fcnya d\u0131\u015f\u0131ndan gelen organik molek\u00fcller birikmi\u015f, bir araya gelerek daha karma\u015f\u0131k yap\u0131lar olu\u015fturmu\u015ftur. Bu a\u015famada polipeptid ve n\u00fckleik asit gibi h\u00fccre i\u00e7erisinde bulunan karma\u015f\u0131k molek\u00fcller olu\u015fmu\u015ftur. Bu molek\u00fcllerden baz\u0131lar\u0131 ilkel canl\u0131l\u0131k \u00f6zellikleri kazanm\u0131\u015flard\u0131r. Canl\u0131l\u0131\u011fa giden yolda \u015fimdilik bu a\u015famaya kadar gelelim. Bundan sonraki sorularda bu ad\u0131mlar\u0131 daha detayl\u0131 \u015fekilde ele alaca\u011f\u0131z. \u015eimdi k\u0131saca canl\u0131l\u0131\u011f\u0131n olu\u015fumuyla ilgili fikirlerin nas\u0131l geli\u015fti\u011fine bakal\u0131m. Bu s\u00fcre\u00e7te birka\u00e7 \u00f6nemli ismin \u00f6ne \u00e7\u0131kt\u0131\u011f\u0131n\u0131 g\u00f6r\u00fcyoruz.<\/p>\n

Canl\u0131l\u0131\u011f\u0131n olu\u015fumu fikirlerinin \u00f6zet bir tarih\u00e7esi<\/strong><\/p>\n

M\u00d6 4. y\u00fczy\u0131lda ya\u015fam\u0131\u015f Aristoteles\u2019in zaman\u0131ndan 19. y\u00fczy\u0131l\u0131n sonlar\u0131na kadar ge\u00e7en 2000 y\u0131l\u0131 a\u015fk\u0131n zaman boyunca, bilim insanlar\u0131 ya\u015fam\u0131n nas\u0131l ortaya \u00e7\u0131kt\u0131\u011f\u0131 konusunda, \u201ckendili\u011finden \u00fcreme\u201d (spontaneous generation) kuram\u0131n\u0131 destekledi. Aristoteles\u2019in daha \u00f6nceki bilim insanlar\u0131n\u0131n g\u00f6zlem ve fikirlerinden yararlanarak olu\u015fturdu\u011fu bu kurama g\u00f6re, canl\u0131 organizmalar cans\u0131z organizmalardan kendili\u011finden ve birdenbire ortaya \u00e7\u0131k\u0131yordu. Bu olu\u015fum her zaman her yerde olmaktayd\u0131. \u00d6rne\u011fin, bir et par\u00e7as\u0131n\u0131 birka\u00e7 g\u00fcn bekletti\u011finizde \u00fczerinde g\u00f6rece\u011finiz kurt\u00e7uklar orada kendili\u011finden meydana geliyordu. Bu kuram\u0131n sonunu getiren \u00e7al\u0131\u015fmalar 17. y\u00fczy\u0131ldan itibaren birikmeye ba\u015flad\u0131 ve bu kurama en \u00f6nemli darbeyi 1859\u2019da Fransiz bilimci Lois Pasteur vurdu. Pasteur, kaynatt\u0131\u011f\u0131 et suyunu uzun ve k\u0131vr\u0131ml\u0131 bir a\u011fza sahip flask i\u00e7erisine koydu. K\u0131vr\u0131m sayesinde d\u0131\u015far\u0131dan i\u00e7eriye hava giriyordu, ancak partik\u00fcller ve mikroorganizmalar giremiyordu. Et suyunda herhangi bir b\u00fcy\u00fcme ger\u00e7ekle\u015fmedi. Ancak flask, mikroorganizmalar\u0131n girebilece\u011fi \u015fekilde yat\u0131r\u0131ld\u0131\u011f\u0131nda, et suyu i\u00e7erisinde h\u0131zl\u0131 bir \u015fekilde b\u00fcy\u00fcme g\u00f6zlemlendi. (\u015eekil 1)<\/p>\n

\"\"
En solda Aristoteles (M\u00d6 384-322), ortada Louis Pasteur (1822-1895) ve en sa\u011fda Pasteur\u2019un deneyinde kulland\u0131\u011f\u0131 flask tipi.<\/figcaption><\/figure>\n

\u201cKendili\u011finden t\u00fcreme\u201d kuram\u0131n\u0131n yo\u011fun olarak tart\u0131\u015f\u0131ld\u0131\u011f\u0131 19. y\u00fczy\u0131lda, Charles Darwin de bu konu \u00fczerinde fikirlerini belirtmi\u015ftir. Ku\u015fkusuz evrim denilince ilk akla gelen isim Charles Darwin\u2019dir. Burada belirtilmesi gereken bir nokta var: Darwin\u2019in evrim kuram\u0131 temel olarak ya\u015fam\u0131n nas\u0131l ba\u015flad\u0131\u011f\u0131 \u00fczerine de\u011fil, nas\u0131l \u00e7e\u015fitlendi\u011fi \u00fczerinedir. Darwin ya\u015fam\u0131n ilk defa nas\u0131l ortaya \u00e7\u0131km\u0131\u015f olabilece\u011fi \u00fczerine \u00e7ok fazla fikir \u00f6ne s\u00fcrmemi\u015ftir. Ancak 1871\u2019de \u0130ngiliz botanik\u00e7i Joseph Dalton Hooker\u2019a yazd\u0131\u011f\u0131 mektupta, ya\u015fam\u0131n ortaya \u00e7\u0131k\u0131\u015f\u0131yla ilgili \u015funlar\u0131 yazm\u0131\u015ft\u0131r: \u201cS\u0131cak su birikintilerinde amonyak, fosfor tuzlar\u0131, \u0131\u015f\u0131k, \u0131s\u0131, elektrik vb. gibi gerekli bile\u015fenler bulundu\u011funda protein yap\u0131s\u0131 olu\u015fturulmu\u015f ve bu pro teinler de daha karma\u015f\u0131k de\u011fi\u015fikliklerin yolunu a\u00e7m\u0131\u015f olabilirler. G\u00fcn\u00fcm\u00fczde b\u00f6yle bir olu\u015fum m\u00fcmk\u00fcn olmayacakt\u0131r, \u00e7\u00fcnk\u00fc cans\u0131z maddelerden olu\u015fturulan yeni karma\u015f\u0131k molek\u00fcl h\u0131zl\u0131ca t\u00fcketilecektir. Yeni bir canl\u0131n\u0131n olu\u015fumu, ortamda ya\u015fayan organizmalar olmad\u0131\u011f\u0131nda m\u00fcmk\u00fcn olmu\u015f olmal\u0131d\u0131r.\u201d<\/p>\n

\u201c\u0130lksel \u00e7orba\u201d kuram\u0131 (primordial soup) <\/strong><\/p>\n

Ya\u015fam\u0131n nas\u0131l ortaya \u00e7\u0131km\u0131\u015f olabilece\u011fi konusu \u00fczerine, Darwin ve Pasteur\u2019un zaman\u0131ndan, Rus bilimci Alexander Oparin\u2019in yeni fikirler \u00f6ne s\u00fcrd\u00fc\u011f\u00fc 1924\u2019e kadar \u00f6nemli bir geli\u015fme olmam\u0131\u015ft\u0131r. Oparin\u2019in g\u00fcn\u00fcm\u00fczde de geni\u015f kabul g\u00f6ren fikirlerine g\u00f6re: \u201cAtmosferik oksijen ya\u015fam\u0131n olu\u015fmas\u0131 i\u00e7in gerekli organik molek\u00fcllerin olu\u015fmas\u0131n\u0131 engelleyecektir. Bu y\u00fczden cans\u0131z maddelerden canl\u0131 organizmalar\u0131n olu\u015fmas\u0131 bir kere olmu\u015ftur, ancak g\u00fcn\u00fcm\u00fczde bu m\u00fcmk\u00fcn de\u011fildir. \u015eu anki atmosferdeki oksijen ve di\u011fer canl\u0131 organizmalar, cans\u0131z molek\u00fcllerden olu\u015facak organik molek\u00fclleri tekrar par\u00e7alayacakt\u0131r. \u0130lk d\u00fcnya ortam\u0131 \u015fimdikinden farkl\u0131yd\u0131. \u0130lk d\u00fcnyan\u0131n oksijensiz ortam\u0131nda, g\u00fcne\u015f \u0131\u015f\u0131\u011f\u0131ndan sa\u011flanan enerji yoluyla organik molek\u00fcllerden olu\u015fan bir \u2018ilksel \u00e7orba\u2019 meydana gelmi\u015ftir. Bu organik molek\u00fcller de zaman i\u00e7erisinde daha karma\u015f\u0131k yap\u0131daki koaservat\u00a0 damlac\u0131klar\u0131 olu\u015fturacaklard\u0131r.<\/p>\n

Bu damlalar birbirleriyle birle\u015ferek b\u00fcy\u00fcyecek ve b\u00f6l\u00fcnerek yeni damlac\u0131klar olu\u015fturacaklard\u0131r. Bu \u015fekilde de yap\u0131n\u0131n devam\u0131n\u0131 korumay\u0131 ama\u00e7layan ilkel metabolik bir yap\u0131 geli\u015ftireceklerdir. Yap\u0131y\u0131 koruyamayan molek\u00fcller ise da\u011f\u0131lacakt\u0131r.\u201d<\/p>\n

Oparin ile ayn\u0131 y\u0131llarda \u0130ngiliz bilimci J. B. S. Haldane de benzer fikirler \u00f6ne s\u00fcrm\u00fc\u015ft\u00fcr. Haldane\u2019e g\u00f6re, D\u00fcnya\u2019n\u0131n ilk zamanlar\u0131ndaki okyanuslarda organik molek\u00fcllerin olu\u015fabilece\u011fi yine ilksel bir \u00e7orba ortam\u0131 olu\u015fmu\u015f olabilir. Biopoiesis olarak adland\u0131r\u0131lan bu fikre g\u00f6re canl\u0131lar, kendini \u00e7o\u011faltabilen cans\u0131z maddelerden olu\u015fmu\u015ftur. Oparin ve Haldane, birbirlerinden ba\u011f\u0131ms\u0131z olarak \u00f6ne s\u00fcrd\u00fckleri fikirleriyle, kendili\u011finden t\u00fcreme kuram\u0131n\u0131n g\u00fcn\u00fcm\u00fcz d\u00fcnya ko\u015fullar\u0131nda ge\u00e7ersiz olaca\u011f\u0131n\u0131 \u00f6ne s\u00fcrm\u00fc\u015flerdir.<\/p>\n

G\u00fcn\u00fcm\u00fczde, ya\u015fam\u0131n nas\u0131l ortaya \u00e7\u0131kt\u0131\u011f\u0131n\u0131 anlatan kuramlar\u0131n hi\u00e7birini kesin olarak do\u011fru kabul edemeyiz. Ancak \u00f6ne s\u00fcr\u00fclen kuramlar aras\u0131nda bilim insanlar\u0131 taraf\u0131ndan en \u00e7ok kabul g\u00f6ren ve deneysel olarak desteklenenleri, Oparin-Haldane taraf\u0131ndan \u00f6ne s\u00fcr\u00fclen \u201cilksel \u00e7orba\u201d kuram\u0131 temeli \u00fczerine kurulmu\u015ftur.<\/p>\n

\"\"
\u0130lk D\u00fcnya ortam\u0131 ya\u015fam i\u00e7in zorlu ko\u015fullara sahipti. Koruyucu bir ozon tabakas\u0131 yoktu ve atmosfer yap\u0131s\u0131 da farkl\u0131yd\u0131. Ancak UV \u0131\u015f\u0131n\u0131, y\u0131ld\u0131r\u0131mlar ve volkanik patlamalar kimyasal reaksiyonlar i\u00e7in gerekli enerjiyi sa\u011fl\u0131yordu.<\/figcaption><\/figure>\n

\u0130ndirgen atmosfer ve birikme<\/strong><\/p>\n

Baz\u0131 bilim insanlar\u0131 ilk D\u00fcnya atmosferinin kimyasal olarak indirgen (reducing) bir ortam oldu\u011funu \u00f6ne s\u00fcrmektedir. Metan, amonyak, su, hidrojen s\u00fclfit, karbondioksit ya da karbonmonoksit ve fosfat bulunurken, molek\u00fcler oksijen ya da ozon bulunmaz ya da \u00e7ok az miktardad\u0131r. Bu t\u00fcr indirgen bir ortamda elektrik enerjisi yoluyla amino asit gibi baz\u0131 basit organik molek\u00fcllerin olu\u015fmas\u0131 katalizlenebilir. Bu durumun olas\u0131l\u0131\u011f\u0131n\u0131 ilk olarak Miller-Urey deneyinde Stanley L. Miller ve Harold C. Urey 1953\u2019de g\u00f6stermi\u015flerdir.<\/p>\n

B\u00f6yle bir ortamda elektron ve hidrojenler inorganik materyali organik yap\u0131lara d\u00f6n\u00fc\u015ft\u00fcrmek i\u00e7in haz\u0131r bulunur. G\u00fcne\u015f enerjisi ve y\u0131ld\u0131r\u0131mlar gerekli enerjiyi sa\u011flayacakt\u0131r. (\u015eekil 2) Organik molek\u00fcller olu\u015fmaya ba\u015flad\u0131ktan sonra birikecektir, \u00e7\u00fcnk\u00fc par\u00e7alanmalar\u0131 i\u00e7in gerekli olan iki etmen ortamda yoktur. Birincisi oksidasyon yoluyla par\u00e7alanmalar\u0131 i\u00e7in gerekli olan oksijen ve di\u011feri ise mikroorganizmalard\u0131r. B\u00f6ylece organik molek\u00fcller birikmeye ba\u015flayacak, yo\u011funla\u015ft\u0131k\u00e7a da birbirleriyle etkile\u015fimleri artacakt\u0131r. Olu\u015fan yeni molek\u00fcllerden baz\u0131lar\u0131 di\u011ferlerine g\u00f6re daha dayan\u0131kl\u0131 olacak, daha \u00e7ok yer tutarak daha fazla zaman var olacaklar ve ya\u015famsal reaksiyonlar ger\u00e7ekle\u015ftirmeye ba\u015flayacaklard\u0131r. Sonu\u00e7 olarak biriken bu molek\u00fcllerin en ba\u015far\u0131l\u0131 olanlar\u0131 kendini kopyalay\u0131p \u00e7o\u011faltabilme yetene\u011fi kazanarak ya\u015fam\u0131n olu\u015fmas\u0131na giden ad\u0131m\u0131 atacakt\u0131r.<\/p>\n

Kaynak:<\/strong> Deniz \u015eahin, 50 Soruda Ya\u015fam\u0131n Tarihi, Bilim ve Gelecek Kitapl\u0131\u011f\u0131, Ekim 2011, 2.Bask\u0131, s.125-131<\/p>\n","protected":false},"excerpt":{"rendered":"

D\u00fcnya \u00fczerinde ilk canl\u0131 organizma birdenbire ortaya \u00e7\u0131kmad\u0131. H\u00fccre olu\u015fmadan \u00f6nce bir\u00e7ok \u00f6nc\u00fc ad\u0131m\u0131n ge\u00e7il mesi gerekti. D\u00fcnya\u2019n\u0131n yakla\u015f\u0131k 4,5 milyar y\u0131l \u00f6nce olu\u015ftu\u011fundan ve canl\u0131l\u0131\u011f\u0131n da yakla\u015f\u0131k 3,5-3,8 milyar y\u0131l \u00f6nce ortaya \u00e7\u0131km\u0131\u015f olmas\u0131 gerekti\u011finden bahsetmi\u015ftik. G\u00f6r\u00fcl\u00fcyor ki, D\u00fcnya olu\u015ftuktan sonra ge\u00e7en 700 milyon-1 milyar y\u0131l kadar s\u00fcre, canl\u0131l\u0131\u011f\u0131n olu\u015fmas\u0131 i\u00e7in gerekli uygun ko\u015fullar\u0131n […]<\/p>\n","protected":false},"author":429,"featured_media":39622,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[19],"tags":[274,200,306,1642,488,595],"class_list":["post-39621","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-bilim-gundemi","tag-dunya","tag-evrim","tag-hucre","tag-molekul","tag-organizma","tag-yasam"],"acf":[],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t