Hospital）
生物谷报道：美国科学家最近成功在实验室构建了原细胞模型，并探索了这些地球最初的细胞如何与周围环境进行相互作用。
原细胞（protocell）是人们对35亿年前地球最原始的生命的设想，它拥有最简单、原始的结构，但却能够构建、复制、容纳DNA。在没有确凿记录的情况下，原细胞计划开辟了一条有效的途径，让人类可以探索地球最早生命的形态、生长和繁殖以及与环境相互作用机制。
在最新研究中，由美国哈佛大学医学院、麻州总医院Jack W. Szostak领导的研究小组发现，由脂肪酸构成的原细胞薄膜可以让环境中的化学物质，包括DNA构建材料进入细胞内部，而无需今天细胞膜运转物质所需的蛋白通道、膜孔或者离子泵。同样，这些原细胞也不需要酶来进行DNA复制。
物质如何进入不具有现代细胞膜运输机制的细胞，一直是个谜团。Jack W. Szostak说，“我们的研究表明，极为原始的细胞或许是从环境中吸收营养，而不必在内部制造这些物质。这支持了两种对立理论的其中之一。”
一些科学家曾提出，远古海底热液区或许是前生分子（prebiotic molecules）的存在地，这些分子包括脂肪酸、氨基酸等。Szostak等人的理论假想表明，脂肪酸可形成于海底矿石的表面，并在间歇泉爆发中被带到地表。当这些脂肪酸处于有水环境中时，它们的亲水端和疏水端都会有序地排列，当水分蒸发后，最终形成了微小的脂肪酸球体——胶团（micelle）。依靠化学浓度和环境的PH值，这些胶团可以形成分层的膜或者囊泡（vesicle）。
研究人员仔细分析了由不同脂肪酸分子构成的囊泡，并且找到了能够让外界分子通过的特殊膜特征。他们发现，尽管较大的DNA或RNA链无法通过脂肪酸膜，但单糖分子和单个核苷酸很容易进入原细胞内部。
当研究人员刚开始工作时，他们并不确定复制原细胞遗传物质所需的材料能够直接进入细胞内。Szostak说，“通过证实这可以发生，而且的确是相当有效地发生，我们离构建能够自我分裂的功能性原细胞的目标又进了一步。”
生物谷推荐原始出处：
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: szostak@molbio.mgh.harvard.edu).
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.
