Predating arizona

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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?

They first attempted to demonstrate that TNA nucleotides could attach by complementary base pairing to a random sequence of DNA, forming a hybrid DNA-TNA strand. Many of the random sequences, however, contained repeated sections of the guanine nucleotide, which had the effect of pausing the transcription of DNA into TNA.

Once random DNA libraries were built excluding guanine, a high yield of DNA-TNA hybrid strands was produced.

Yet according to John Chaput, a researcher at the Center for Evolutionary Medicine and Informatics, at Arizona State University’s Biodesign Institute, it may not always have been so.

Chaput and other researchers studying the first tentative flickering of life on earth have investigated various alternatives to familiar genetic molecules.

They are simpler than the five-carbon pentose sugars found in both DNA and RNA and could assemble more easily in a prebiotic world, from two identical two-carbon fragments.

This advantage in structural simplicity was originally thought to be an Achilles’ heel for TNA, making its binding behavior incompatible with DNA and RNA.

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Chaput suggests that issues concerning the prebiotic synthesis of ribose sugars and the non-enzymatic replication of RNA may provide circumstantial evidence of an earlier genetic system more readily produced under primitive earth conditions.

According to Chaput, one interesting contender for the role of early genetic carrier is a molecule known as TNA, whose arrival on the primordial scene may have predated its more familiar kin.

A nucleic acid similar in form to both DNA and RNA, TNA differs in the sugar component of its structure, using threose rather than deoxyribose (as in DNA) or ribose (as in RNA) to compose its backbone.

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.

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