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   Original article :   
      
   https://scitechdaily.com/discovery-supports-a-surprising-new-view-of-how-life-o   
   n-earth-originated/   
      
      
      
      
   Discovery Supports a Surprising New View of How Life on Earth Originated   
   TOPICS:DNAGeneticsPopularRNAScripps Research Institute   
   By SCRIPPS RESEARCH INSTITUTE DECEMBER 28, 2020   
      
   Newly described chemical reaction could have assembled DNA building blocks   
   before life forms and their enzymes existed.   
      
   Discovery boosts theory that life on our planet arose from RNA-DNA mix.   
   Chemists at Scripps Research have made a discovery that supports a surprising   
   new view of how life originated on our planet.   
      
   In a study published in the chemistry journal Angewandte Chemie, they   
   demonstrated that a simple compound called diamidophosphate (DAP), which was   
   plausibly present on Earth before life arose, could have chemically knitted   
   together tiny DNA building blocks called deoxynucleosides into strands of   
   primordial DNA.   
      
   The finding is the latest in a series of discoveries, over the past several   
   years, pointing to the possibility that DNA and its close chemical cousin RNA   
   arose together as products of similar chemical reactions, and that the first   
   self-replicating molecules — the first life forms on Earth — were mixes   
   of the two.   
      
      
   The 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 on Earth first arose. In particular, it paves the way for more   
   extensive studies of how self-replicating DNA-RNA mixes could have evolved   
   and spread on the primordial Earth and ultimately seeded the more mature   
   biology of modern organisms.   
      
   “This finding is an important step toward the development of a detailed   
   chemical model of how the first life forms originated on Earth,” says study   
   senior author Ramanarayanan Krishnamurthy, PhD, associate professor of   
   chemistry at Scripps Research.   
      
   The finding also nudges the field of origin-of-life chemistry away from the   
   hypothesis that has dominated it in recent decades: The “RNA World”   
   hypothesis posits that the first replicators were RNA-based, and that DNA   
   arose only later as a product of RNA life forms.   
      
   Is RNA too sticky?   
   Krishnamurthy and others have doubted the RNA World hypothesis in part   
   because RNA molecules may simply have been too “sticky” to serve as the   
   first self-replicators.   
      
   A strand of RNA can attract other individual RNA building blocks, which stick   
   to it to form a sort of mirror-image strand — each building block in the   
   new strand binding to its complementary building block on the original,   
   “template” strand. If the new strand can detach from the template strand,   
   and, by the same process, start templating other new strands, then it has   
   achieved the feat of self-replication that underlies life.   
      
   But while RNA strands may be good at templating complementary strands, they   
   are not so good at separating from these strands. Modern organisms make   
   enzymes that can force twinned strands of RNA — or DNA — to go their   
   separate ways, thus enabling replication, but it is unclear how this could   
   have been done in a world where enzymes didn’t yet exist.   
      
   A chimeric workaround   
   Krishnamurthy and colleagues have shown in recent studies that “chimeric”   
   molecular strands that are part DNA and part RNA may have been able to get   
   around this problem, because they can template complementary strands in a   
   less-sticky way that permits them to separate relatively easily.   
      
   The chemists also have shown in widely cited papers in the past few years   
   that the simple ribonucleoside and deoxynucleoside building blocks, of RNA   
   and DNA respectively, could have arisen under very similar chemical   
   conditions on the early Earth.   
      
   Moreover, in 2017 they reported that the organic compound DAP could have   
   played the crucial role of modifying ribonucleosides and stringing them   
   together into the first RNA strands. The new study shows that DAP under   
   similar conditions could have done the same for DNA.   
      
   “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,” says first author Eddy Jiménez, PhD, a postdoctoral research   
   associate in the Krishnamurthy lab.   
      
   “Now that we understand better how a primordial chemistry could have made   
   the first RNAs and DNAs, we can start using it on mixes of ribonucleoside and   
   deoxynucleoside building blocks to see what chimeric molecules are formed —   
   and whether they can self-replicate and evolve,” Krishnamurthy says.   
      
   He notes that the work may also have broad practical applications. The   
   artificial synthesis of DNA and RNA — for example in the “PCR”   
   technique that underlies COVID-19 tests — amounts to a vast global   
   business, but depends on enzymes that are relatively fragile and thus have   
   many limitations. Robust, enzyme-free chemical methods for making DNA and RNA   
   may end up being more attractive in many contexts, Krishnamurthy says.   
      
   Reference: “Prebiotic Phosphorylation and Concomitant Oligomerization of   
   Deoxynucleosides to form DNA” by Eddy Jiménez, Clémentine Gibard and   
   Ramanarayanan Krishnamurthy, 15 December 2020, Angewandte Chemie.   
   DOI: 10.1002/anie.202015910   
      
   Funding was provided by the Simons Foundation.   
      
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