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Discovery supports surprising new ideas about the origin of life on Earth



Genetic sequencing concept

The newly described chemical reactions may have assembled DNA building blocks before the existence of life forms and their enzymes.

The discovery pushed the theory that life on our planet originated from a mixture of RNA and DNA.

Chemists at Scripps Research made a discovery that supports a surprising new view of how life originated on our planet.

In a study published in a chemical journal Applied Chemistry, They proved that a simple compound called phosphorodiamidate (DAP), which may have existed on the earth before life appeared, can be chemically weaved together DNA Structural units called deoxynucleosides enter the original DNA strand.

The discovery is the latest in a series of discoveries in the past few years, pointing to the possibility of DNA and its close chemical cousins. Ribonucleic acid Appeared together as products of similar chemical reactions, and the first self-replicating molecule (the first life form on Earth) was a mixture of the two.

This discovery may also bring new practical applications in chemistry and biology, but its main significance is that it solves the ancient problem of how life on earth first appeared. In particular, it paved the way for a wider range of research involving how self-replicating DNA-RNA mixtures evolved and spread on the primordial earth, and ultimately injected the seeds for the more mature biology of modern organisms.

Dr. Ramanarayanan Krishnamurthy, associate professor of chemistry at Scripps Research and senior author of the study, said: “This discovery is an important step in establishing a detailed chemical model that is about the origin of the first life on Earth.

This discovery has also moved the field of life chemistry away from the hypothesis that has been dominant in recent decades: the “RNA World”

; hypothesis assumes that the first replicon is based on RNA, and DNA only later appears as a product of RNA life forms.

Is RNA too sticky?

Krishnamurthy and others questioned the hypothesis of the “RNA World”, partly because RNA molecules may be too “sticky” to act as the first self-replicator.

RNA strands can attract other single RNA building blocks and stick to them to form a kind of mirror image strand-each building block in the new strand binds to a complementary building block on the original “template” strand. If the new chain can be separated from the template chain and start to template other new chains through the same process, then it has achieved the feat of self-replication that constitutes life.

However, although RNA strands may be good at templated complementary strands, they are not good at separating from these strands. Enzymes produced by modern organisms can force the double strands of RNA or DNA to separate, thereby achieving replication, but it is not clear how to do this in a world without enzymes.

Mosaic solution

Krishnamurthy and colleagues have shown in recent studies that “chimeric” molecular strands of part of DNA and part of RNA may have solved this problem because they can template complementary strands in a less sticky way, thereby making them Separated relatively easily. .

Chemists have also shown in widely cited papers in the past few years that simple ribonucleosides and deoxyribonucleic acids (RNA and DNA, respectively) may have appeared on the early earth when the chemical and chemical conditions were very similar. ).

In addition, in 2017, they reported that the organic compound DAP may have played a key role in modifying ribonucleosides and stringing them together to form the first RNA strand. This new study shows that DAP under similar conditions can have the same effect on DNA.

“What surprises us is that when the deoxynucleosides are not exactly the same, but a mixture of different DNA’letters’ (such as A and T or G and C, such as real DNA), the reaction of DAP with deoxynucleosides will be more Good,” said first author Dr. Eddy Jiménez, a postdoctoral researcher in Krishnamurti’s laboratory.

“Now that we have a better understanding of how the original chemical methods produced the first batch of RNA and DNA, we can start using them for the mixture of ribonucleosides and deoxynucleoside building blocks to see which chimeras are formed. Molecules, and whether they can replicate and evolve themselves, Krishnamurti said.

He pointed out that this work may also have a wide range of practical applications. Artificial synthesis of DNA and RNA-such as the basic “PCR” technology Coronavirus disease Testing-involves a huge global business, but depends on relatively fragile enzymes, so there are many limitations. Krishnamurthy says reliable, enzyme-free chemical methods for making DNA and RNA may end up being more attractive in many cases.

Reference: Eddy Jiménez, Clémentine Gibard and Ramanarayanan Krishnamurthy, “Phosphorylation of prebiotics and accompanying oligomerization to form DNA”, December 15, 2020, Applied Chemistry.
DOI: 10.1002 / anie.202015910

Funding was provided by the Simmons Foundation.




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