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英国化学家13日宣布，他们开发出一个实验模型，可展示40亿年前地球生命如何以一种自我复制的分子形式起源。研究人员在早期地球环境模拟条件下首次合成了一种中间物质，该物质可纯化合成RNA所需的核糖和碱基，并最终形成一种类RNA。相关研究发表在当日出版的《自然》杂志上。 众所周知，脱氧核糖核酸（DNA）和核糖核酸（RNA）是生物体的遗传分子，都由碱基、核糖和磷酸组成。DNA具有双螺旋的复杂结构，而单链的RNA在结构上更为简单和牢固。因此有学者认为，DNA过于复杂，不可能在瞬间突然出现。在生命最初产生时，DNA的单链“表亲”———RNA要先于DNA出现，是地球上最早出现的携带遗传信息的核酸。 不过，这种“RNA第一”理论，在现实论证中却遇到不少问题。 RNA包括三个主要组成部分：碱基、核糖和磷酸。在传统思路看来，这三种物质必须分别形成后再以分子的形式相结合才能形成RNA。因此与DNA相比，RNA虽然更为简单，但仍是一个复杂分子，不大可能自行组装成功。此前试图通过化学方式来证明这三种化学物质可以同时产生的努力也均以失败告终。 但英国曼彻斯特大学化学家给出了不同解释。由约翰·萨瑟兰教授领导的研究小组大胆提出，通过模拟地球早期环境中的一系列化学反应，可以合成一种重要的中间物质，进而合成类RNA。 实验模型表明，从40亿年前就已在地球上存在的简单化学物质中形成RNA的所有成分是完全可能的，他们已合成了RNA的三个组成部分中的两个，并首次成功合成出一种类RNA。试验先由一种被称为羟基乙醛的简单糖类开始，而后将其与一种氰化物和氨的合成物———单氢胺以及磷酸盐发生反应，从而产生出一种被称为2-氨基噁唑的中间物质。研究人员发现，自然界的昼夜温差可帮助纯化2-氨基噁唑，将其变成充裕的前体，这有助于形成新核苷酸分子的糖和碱基蛋白。磷酸盐的存在和来自太阳的紫外线则促成了合成。 美国分子生物学家杰克?索斯塔克在《自然》杂志的相关评论中，对该研究给予了高度评价,称这将是多年来通过化学方式解释生命起源研究的一大进展，代表了多年来“前生物化学”研究所取得的重大进展，前生物化学是研究导致地球生物出现的化学进程的术语。 推荐原始出处： Nature 459, 239-242 (14 May 2009) | doi:10.1038/nature08013 Synthesis of activated pyrimidine ribonucleotides in prebiotically plausible conditions Matthew W. Powner1, Béatrice Gerland1 & John D. Sutherland1 1 School of Chemistry, The University of Manchester, Oxford Road, Manchester M13 9PL, UK At some stage in the origin of life, an informational polymer must have arisen by purely chemical means. According to one version of the 'RNA world' hypothesis1, 2, 3 this polymer was RNA, but attempts to provide experimental support for this have failed4, 5. In particular, although there has been some success demonstrating that 'activated' ribonucleotides can polymerize to form RNA6, 7, it is far from obvious how such ribonucleotides could have formed from their constituent parts (ribose and nucleobases). Ribose is difficult to form selectively8, 9, and the addition of nucleobases to ribose is inefficient in the case of purines10 and does not occur at all in the case of the canonical pyrimidines11. Here we show that activated pyrimidine ribonucleotides can be formed in a short sequence that bypasses free ribose and the nucleobases, and instead proceeds through arabinose amino-oxazoline and anhydronucleoside intermediates. The starting materials for the synthesis—cyanamide, cyanoacetylene, glycolaldehyde, glyceraldehyde and inorganic phosphate—are plausible prebiotic feedstock molecules12, 13, 14, 15, and the conditions of the synthesis are consistent with potential early-Earth geochemical models. Although inorganic phosphate is only incorporated into the nucleotides at a late stage of the sequence, its presence from the start is essential as it controls three reactions in the earlier stages by acting as a general acid/base catalyst, a nucleophilic catalyst, a pH buffer and a chemical buffer. For prebiotic reaction sequences, our results highlight the importance of working with mixed chemical systems in which reactants for a particular reaction step can also control other steps. (责任编辑：Doctor001) |
