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生物谷報道：美國科學(xué)家最近成功在實驗室構(gòu)建了原細胞模型，并探索了這些地球最初的細胞如何與周圍環(huán)境進行相互作用,。
原細胞（protocell）是人們對35億年前地球最原始的生命的設(shè)想,，它擁有最簡單,、原始的結(jié)構(gòu),，但卻能夠構(gòu)建,、復(fù)制、容納DNA,。在沒有確鑿記錄的情況下,，原細胞計劃開辟了一條有效的途徑，讓人類可以探索地球最早生命的形態(tài),、生長和繁殖以及與環(huán)境相互作用機制。
在最新研究中,，由美國哈佛大學(xué)醫(yī)學(xué)院,、麻州總醫(yī)院Jack W. Szostak領(lǐng)導(dǎo)的研究小組發(fā)現(xiàn)，由脂肪酸構(gòu)成的原細胞薄膜可以讓環(huán)境中的化學(xué)物質(zhì),，包括DNA構(gòu)建材料進入細胞內(nèi)部,，而無需今天細胞膜運轉(zhuǎn)物質(zhì)所需的蛋白通道、膜孔或者離子泵,。同樣,，這些原細胞也不需要酶來進行DNA復(fù)制。
物質(zhì)如何進入不具有現(xiàn)代細胞膜運輸機制的細胞,，一直是個謎團,。Jack W. Szostak說，“我們的研究表明,，極為原始的細胞或許是從環(huán)境中吸收營養(yǎng),，而不必在內(nèi)部制造這些物質(zhì)。這支持了兩種對立理論的其中之一,。”
一些科學(xué)家曾提出,，遠古海底熱液區(qū)或許是前生分子（prebiotic molecules）的存在地，這些分子包括脂肪酸,、氨基酸等,。Szostak等人的理論假想表明，脂肪酸可形成于海底礦石的表面,，并在間歇泉爆發(fā)中被帶到地表,。當這些脂肪酸處于有水環(huán)境中時，它們的親水端和疏水端都會有序地排列,，當水分蒸發(fā)后,，最終形成了微小的脂肪酸球體——膠團（micelle）。依靠化學(xué)濃度和環(huán)境的PH值,，這些膠團可以形成分層的膜或者囊泡（vesicle）,。
研究人員仔細分析了由不同脂肪酸分子構(gòu)成的囊泡，并且找到了能夠讓外界分子通過的特殊膜特征,。他們發(fā)現(xiàn),，盡管較大的DNA或RNA鏈無法通過脂肪酸膜,，但單糖分子和單個核苷酸很容易進入原細胞內(nèi)部。
當研究人員剛開始工作時,，他們并不確定復(fù)制原細胞遺傳物質(zhì)所需的材料能夠直接進入細胞內(nèi),。Szostak說，“通過證實這可以發(fā)生,，而且的確是相當有效地發(fā)生,，我們離構(gòu)建能夠自我分裂的功能性原細胞的目標又進了一步。”
生物谷推薦原始出處：
Nature,，doi:10.1038/nature07018,，Sheref S. Mansy, Jack W. Szostak
Template-directed synthesis of a genetic polymer in a model protocell
Sheref S. Mansy1, Jason P. Schrum1, Mathangi Krishnamurthy1, Sylvia Tobé1, Douglas A. Treco1 & Jack W. Szostak1
Howard Hughes Medical Institute, Department of Molecular Biology and the Center for Computational and Integrative Biology, Massachusetts General Hospital, Boston, Massachusetts 02114, USA
Correspondence to: Jack W. Szostak1 Correspondence and requests for materials should be addressed to J.W.S. (Email: [email protected]).
Contemporary phospholipid-based cell membranes are formidable barriers to the uptake of polar and charged molecules ranging from metal ions to complex nutrients. Modern cells therefore require sophisticated protein channels and pumps to mediate the exchange of molecules with their environment. The strong barrier function of membranes has made it difficult to understand the origin of cellular life and has been thought to preclude a heterotrophic lifestyle for primitive cells. Although nucleotides can cross dimyristoyl phosphatidylcholine membranes through defects formed at the gel-to-liquid transition temperature1, 2, phospholipid membranes lack the dynamic properties required for membrane growth. Fatty acids and their corresponding alcohols and glycerol monoesters are attractive candidates for the components of protocell membranes because they are simple amphiphiles that form bilayer membrane vesicles3, 4, 5 that retain encapsulated oligonucleotides3, 6 and are capable of growth and division7, 8, 9. Here we show that such membranes allow the passage of charged molecules such as nucleotides, so that activated nucleotides added to the outside of a model protocell spontaneously cross the membrane and take part in efficient template copying in the protocell interior. The permeability properties of prebiotically plausible membranes suggest that primitive protocells could have acquired complex nutrients from their environment in the absence of any macromolecular transport machinery; that is, they could have been obligate heterotrophs.
