新的证据支持地球上的生命起源于RNA-DNA混合物的理论

新的证据支持地球上的生命起源于RNA-DNA混合物的理论

For a long time, the “RNA World” hypothesis has been widely accepted by chemists and molecular biologists as to how life on Earth arose. First proposed by Alexander Rich in 1962, this hypothesis suggests that primordial self-replicating RNA arose before proteins and DNA. However, there have been recent studies contradicting this hypothesis, proposing that RNA and DNA may have in fact formed together.

很长一段时间以来，关于地球上的生命是如何产生的，“RNA世界”假说被化学家和分子生物学家广泛接受。这个假说最早由亚历山大·里奇在1962年提出，它认为原始的自我复制RNA出现在蛋白质和DNA之前。然而，最近有研究反驳了这一假说，提出RNA和DNA实际上可能是一起形成的。

A new study published in the journal Angewandte Chemie has joined this opposition, suggesting that RNA and DNA originated together from similar chemical reactions and that the first self-replicating molecules may have been a DNA/RNA mixture. “This finding is an important step toward the development of a detailed chemical model of how the first life forms originated on Earth,” Dr Ramanarayanan Krishnamurthy, associate professor of chemistry at Scripps Research Institute and senior author of the study, said in a statement.

发表在《Angewandte Chemie》杂志上的一项新研究也加入了这一反对意见，指出RNA和DNA共同起源于类似的化学反应，并且第一个自我复制的分子可能是DNA/RNA的混合物。斯克里普斯研究所化学副教授、该研究的资深作者拉马纳拉亚南·克里希那穆尔蒂博士在一份声明中表示:“这一发现是朝着建立有关地球上最初生命形式起源的详细化学模型迈出的重要一步。”

Francesca Benson MSci

The authors of the paper state that RNA might be too “sticky” to have been the first self-replicating molecules. RNA strands replicate by one strand serving as a template for a complementary strand, which in present organisms is separated from the template by enzymes. However, RNA strands are not good at separating by themselves, and enzymes are proteins and therefore would not have existed in the “RNA World”. The researchers claim that “chimeric” strands, made of both RNA and DNA, could circumvent this problem by being less sticky.

该论文的作者指出，RNA可能太“粘”了，不可能是第一个自我复制的分子。RNA链由单链复制，作为互补链的模板，在目前的生物中，互补链是由酶从模板中分离出来的。然而，RNA链并不善于自我分离，酶是蛋白质，因此在“RNA世界”中不存在。研究人员声称，由RNA和DNA组成的“嵌合”链可以通过降低粘性来规避这个问题。

In the study, the researchers built on previous studies of RNA and DNA formation in prebiotic (before life) conditions. These conditions do not include chemicals that only occur due to living organisms, only abiotic ones. This allows researchers to assess how life could have arisen from these abiotic conditions. This study focused on nucleosides – the building blocks of RNA and DNA – in the presence of the organic compounds 2-aminoimidazole and Diamidophosphate (DAP).

在这项研究中，研究人员基于之前在生命前条件下RNA和DNA形成的研究。这些条件不包括只发生在活的有机体，只有非生物的化学物质。这使得研究人员能够评估生命是如何从这些非生物条件中产生的。这项研究的重点是核苷——RNA和DNA的组成部分——在有机化合物2-氨基咪唑和磷酸二胺(DAP)存在的情况下。

It was observed that, with both of these chemicals, deoxynucleosides (which make up DNA) reacted to produce short oligomers of DNA. Preliminary data indicated that the same occurred for ribonucleosides, which make up RNA. In a 2017 study, Krishnamurthy and colleagues showed that DAP could have played a key role in modifying ribonucleosides to string them together into the first RNA strands. The new study found under similar conditions it may do the same for DNA.

据观察，这两种化学物质，脱氧核苷(组成DNA)反应产生短的DNA寡聚体。初步数据表明，构成RNA的核糖核苷也发生了同样的情况。在2017年的一项研究中，Krishnamurthy和同事表明，DAP可能在修饰核糖核酸苷，将它们串成第一个RNA链方面发挥了关键作用。新的研究发现，在类似的条件下，它可能对DNA起同样的作用。

“We found, to our surprise, that using DAP to react with deoxynucleosides works better when the deoxynucleosides are not all the same but are instead mixes of different DNA 'letters' such as A and T, or G and C, like real DNA,” explained first author Dr Eddy Jiménez.

令我们吃惊的是,“我们发现使用DAP和deoxynucleosides反应可以更美好,即使你的deoxynucleosides并不都是一样的,而是混合了不同的DNA“字母”如和T、G和C,像真正的DNA,”第一作者艾迪吉梅内斯博士解释道。

These results could give us more clarity as to how life on Earth originated, as well as being useful for research and industry. Many processes – such as polymerase chain reaction (PCR), used in testing for COVID-19 – rely on the artificial synthesis of DNA and RNA, but are reliant on often fragile enzymes. These findings could lead to enzyme-free alternative methods.

这些结果可以让我们更清楚地了解地球上的生命是如何起源的，对研究和工业也很有用。许多程序，如用于检测COVID-19的聚合酶链反应(PCR)，都依赖于DNA和RNA的人工合成，但往往依赖于脆弱的酶。这些发现可能导致不含酶的替代方法。