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The two nucleic acids DNA and RNA are named for the type of sugar complex that forms each molecule’s sugar-phosphate backbone – a kind of molecular thread holding the nucleotide beads together.
Could a simpler, self-replicating molecule have existed as a precursor to RNA, perhaps providing genetic material for earth’s earliest organisms?
In the chemistry of the living world, a pair of nucleic acids – DNA and RNA – reign supreme.
As carrier molecules of the genetic code, they provide all organisms with a mechanism for faithfully reproducing themselves as well as generating the myriad proteins vital to living systems.
While the iconic double helix of DNA is formed from two complimentary strands of nucleotides, attached to each other by base pairing in a helical staircase, RNA is single-stranded.The sequences obtained were 70 nucleotides in length, long enough Chaput says, to permit them to fold into shapes with defined binding sites.The DNA-TNA hybrids were then incubated with the target molecule thrombin.Although solid proof that TNA acted as an RNA precursor in the prebiotic world may be tricky to obtain, Chaput points to the allure of this molecule as a strong candidate, capable of storing information, undergoing selection processes and folding into tertiary structures that can perform complex functions.This result provides the motivation to explore TNA as an early genetic system.In an article released online in the journal Nature Chemistry, Chaput and his group describe the Darwinian evolution of functional TNA molecules from a large pool of random sequences.This is the first case where such methods have been applied to molecules other than DNA and RNA, or very close structural analogues thereof.Chaput’s experiments with the nucleic acid TNA provide an attractive case.To begin with, TNA uses tetrose sugars, named for the four-carbon ring portion of their structure.Surprisingly, however, research has now shown that a single strand of TNA can indeed bind with both DNA and RNA by Watson-Crick base pairing – a fact of critical importance if TNA truly existed as a transitional molecule capable of sharing information with more familiar nucleic acids that would eventually come to dominate life.In the current study, Chaput and his group use an approach known as molecular evolution to explore TNA’s potential as a genetic biomolecule.