Theoretical origin of life: early molecules for life (Introduction)

by David Turell , Thursday, February 25, 2016, 00:50 (3194 days ago) @ David Turell

Another review article, which does not advance the theory: - https://www.quantamagazine.org/20160216-how-to-build-life-in-a-pre-darwinian-world/ - "However, scientists have found it surprisingly challenging to create self-replicating RNA in the lab. Researchers have had some success, but the candidate molecules they have manufactured to date can only replicate certain sequences or a certain length of RNA. Moreover, these RNA molecules are themselves quite complicated, raising the question of how they might have formed through chance chemical means. (my bold)
*** - "At the heart of Hud's proposal is a chemical means for generating a rich diversity of proto-life. Computer simulations show that certain chemical conditions can produce a varied collection of RNA-like molecules. And the team is currently testing the idea with real molecules in the lab; they hope to publish the results soon. - *** - "Hud's group is leading the way for a number of researchers who are challenging the traditional RNA-world hypothesis and its reliance on biological rather than chemical evolution. In the traditional model, new molecular machinery was created using biological catalysts, known as enzymes, as is the case in modern cells. In Hud's proto-life stage, myriad RNA or RNA-like molecules could form and change through purely chemical means. “Chemical evolution could have helped life get started without enzymes,” Hud said. - *** - "Carl Woese, a renowned biologist who gave us the modern tree of life, believed that the Darwinian era was preceded by an early phase of life governed by very different evolutionary forces. Woese thought it would have been nearly impossible for an individual cell to spontaneously come up with everything it needed for life. So he envisioned a rich diversity of molecules engaged in a communal existence. Rather than competing with each other, primitive cells shared the molecular innovations they invented. Together, the pre-Darwinian pool created the components needed for complex life, priming the early Earth for the emergence of the magnificent menagerie we see today. (Woese discovered Archaia) - *** - "In Hud's vision of a prebiotic world, the primordial RNA soup underwent regular cycles of heating and cooling in a thick, viscous solution. Heat separated the bound pairs of RNA, and the viscous solution kept the separated molecules apart for a while. In the interim, small segments of RNA, just a few letters in length, stuck to each long strand. The small segments eventually got sewn together, forming a new strand of RNA that matched the original long strand. The cycle then began again. - "Over time, a pool of varied RNA-like molecules would have accumulated, some of them capable of simple functions, such as metabolism. And just like that, purely chemical reactions would have produced the molecular diversity needed to create Woese's pre-Darwinian cornucopia of proto-life. - "Hud's team has been able to carry out the first stages of the replication process in the laboratory, although they can't yet glue together the short segments without resorting to biological tools. If they can get over that hurdle, they'll have created a versatile way of replicating any RNA that pops up. - 
*** - "Despite the powerful evidence, it's still hard to imagine how the ribosomal core could have been created by chemical evolution. An enzyme that makes more of itself — like the replicator RNA of the RNA-world hypothesis — automatically creates a feedback loop, continually boosting its own production. By contrast, the ribosomal core doesn't produce more ribosomal cores. It produces random chains of amino acids. It's unclear how this process would encourage the production of more ribosomes. “Why would making random peptides make that thing better?” Higgs said. (Another complication) - "Hud and his collaborators propose that RNA and proteins evolved in tandem, and those that figured out how to work together survived best. This idea lacks the simplicity of the RNA world, which posits a single molecule capable of both encoding information and catalyzing chemical reactions." - Comment: More complex, and more wishful thinking. Read it all to sense the frustration.