新的證據(jù)支持地球上的生命起源于RNA-DNA混合物的理論

新的證據(jù)支持地球上的生命起源于RNA-DNA混合物的理論

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.

很長一段時間以來，關(guān)于地球上的生命是如何產(chǎn)生的，“RNA世界”假說被化學(xué)家和分子生物學(xué)家廣泛接受。這個假說最早由亞歷山大·里奇在1962年提出，它認(rèn)為原始的自我復(fù)制RNA出現(xiàn)在蛋白質(zhì)和DNA之前。然而，最近有研究反駁了這一假說，提出RNA和DNA實際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.

發(fā)表在《Angewandte Chemie》雜志上的一項新研究也加入了這一反對意見，指出RNA和DNA共同起源于類似的化學(xué)反應(yīng)，并且第一個自我復(fù)制的分子可能是DNA/RNA的混合物。斯克里普斯研究所化學(xué)副教授、該研究的資深作者拉馬納拉亞南·克里希那穆爾蒂博士在一份聲明中表示:“這一發(fā)現(xiàn)是朝著建立有關(guān)地球上最初生命形式起源的詳細(xì)化學(xué)模型邁出的重要一步。”

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.

該論文的作者指出，RNA可能太“粘”了，不可能是第一個自我復(fù)制的分子。RNA鏈由單鏈復(fù)制，作為互補鏈的模板，在目前的生物中，互補鏈?zhǔn)怯擅笍哪０逯蟹蛛x出來的。然而，RNA鏈并不善于自我分離，酶是蛋白質(zhì)，因此在“RNA世界”中不存在。研究人員聲稱，由RNA和DNA組成的“嵌合”鏈可以通過降低粘性來規(guī)避這個問題。

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).

在這項研究中，研究人員基于之前在生命前條件下RNA和DNA形成的研究。這些條件不包括只發(fā)生在活的有機體，只有非生物的化學(xué)物質(zhì)。這使得研究人員能夠評估生命是如何從這些非生物條件中產(chǎn)生的。這項研究的重點是核苷——RNA和DNA的組成部分——在有機化合物2-氨基咪唑和磷酸二胺(DAP)存在的情況下。

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.

據(jù)觀察，這兩種化學(xué)物質(zhì)，脫氧核苷(組成DNA)反應(yīng)產(chǎn)生短的DNA寡聚體。初步數(shù)據(jù)表明，構(gòu)成RNA的核糖核苷也發(fā)生了同樣的情況。在2017年的一項研究中，Krishnamurthy和同事表明，DAP可能在修飾核糖核酸苷，將它們串成第一個RNA鏈方面發(fā)揮了關(guān)鍵作用。新的研究發(fā)現(xiàn)，在類似的條件下，它可能對DNA起同樣的作用。

“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.

令我們吃驚的是,“我們發(fā)現(xiàn)使用DAP和deoxynucleosides反應(yīng)可以更美好,即使你的deoxynucleosides并不都是一樣的,而是混合了不同的DNA“字母”如和T、G和C,像真正的DNA,”第一作者艾迪吉梅內(nèi)斯博士解釋道。

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.

這些結(jié)果可以讓我們更清楚地了解地球上的生命是如何起源的，對研究和工業(yè)也很有用。許多程序，如用于檢測COVID-19的聚合酶鏈反應(yīng)(PCR)，都依賴于DNA和RNA的人工合成，但往往依賴于脆弱的酶。這些發(fā)現(xiàn)可能導(dǎo)致不含酶的替代方法。