Discovery fosters the theory that life on Earth originated from RNA-DNA fusion

The chemists at Scripps Research have made a discovery that supports a surprisingly new view of how life originated on our planet.

In a study published in the journal Chemistry Engandte Chemi, They showed that a simple compound called diamidophosphate (DAP), which was reasonably present on Earth before life arose, could be chemically integrated small DNA building blocks called deoxynucleosides, known in primitive DNA.

The discovery is the latest in a series of discoveries over the past few years, pointing to the possibility that DNA and its close chemical cousin RNA came together as products of similar chemical reactions, and the first self-replicating molecules-first life forms on Earth were a combination of the two. .

This discovery may also lead to new practical applications in chemistry and biology, but its main significance is that it addresses the age-old question of how life originated on Earth. In particular, how it replicates self-replicating DNA-RNA. The combination paves the way for a more comprehensive study of what could have evolved on primitive Earth and ultimately the more mature biology of modern organisms.

“This discovery is an important step towards the development of a detailed chemical model of how the first form of life originated on Earth,” says Ramanarayana Krishnamurthy, associate professor of chemistry at Scripps Research.

These findings also push the field of chemistry of life based on it into the present decades: the “RNA World” hypothesis demonstrates that the first replicas of RNA. Were based, and DNA. Emerged only after production. RNA is a form of life.

What is RNA? Too sticky?

Krishnamurthy and others have questioned the RNA World hypothesis in part because RNA molecules can be too “sticky” to serve only as first self-replicators.

The strand of RNA is another individual RNA. Can attract building blocks, sticking to it to form a kind of mirror-image strand – each building block in the new strand binds its complementary building block to the original, “template” strand. If the new strand can be separated from the sample strand, and by the same process, begin to template other new strands, then it achieves the feat of self-replication that subjugates life.

But while RNA strands may be good at templating complementary strands, they are not as good at separating from these strands. Modern organisms produce enzymes that attach to RNA. Or DNA may force twin strands to move in different ways, thus enabling replication, but it is unclear how this could have happened in a world where these enzymes did not yet exist.

Chimeric workround

Recent studies by Krishnamurthy and colleagues have shown that “chimeric” molecular strands that are part DNA and part RNA can cope with this problem, as they can sample complementary strands in a less-sticky way that allows them to separate relatively easily. .

Chemists have also shown in papers widely cited over the past few years that RNA and DNA, simple ribunucleoside and deoxynucleoside building blocks, respectively, can occur in very similar chemical conditions on early Earth.

Moreover, in 2017 they reported that the organic compound DAP would have played a crucial role in modifying the ribonucleosides and drawing them together in the first RNA strands. A new study shows that DAP would have done the same for DNA under similar conditions.

“We are surprised that the use of DAP to react with deoxynucleotides works better when deoxynucleotides are not all the same, but instead a combination of different DNA‘ characters ’like D and N, or G and C, e.g. That real DNA, “Post-Doctoral Research Associate Ph.D. Says, first author Eddie Jimenez.

“Now that we better understand how ancient chemistry first created RNA and DNA, we can start using it on a combination of ribonucleoside and deoxynucleoside building blocks to see how chemically molecules form – and that self. – Whether it can be copied and developed or not, “says Krishnamurti.

He notes that the work may also have a wide range of practical applications. The synthetic synthesis of DNA and RNA – for example in the “PCR” technique that includes COVID-19 tests – is similar for global trade, but it is based on enzymes that are relatively fragile and therefore have many limitations. Krishnamurti says strong, enzyme-free chemical methods for making DNA and RNA can be more attractive in many respects.