tag:blogger.com,1999:blog-1943438907128937267.post8402594039390509754..comments2023-07-14T00:55:35.451-07:00Comments on Darwin's Doubt Critical Reviews: Signature in the Cell?Unknownnoreply@blogger.comBlogger3125tag:blogger.com,1999:blog-1943438907128937267.post-28218308724778339952014-10-21T08:27:21.727-07:002014-10-21T08:27:21.727-07:00Rather than "it stops at the threshold,"...Rather than "it stops at the threshold," it would have been more accurate to say that Poole et. al. jumped over the protein takeover and went on to talk about such things as the following:<br /><br />"Our model for the genome of the last ribo-organism<br />(Jeffares et al. 1997) is consistent with the hypothesis we<br />propose here—that the last universal common ancestor<br />had a genome that was more eukaryote-like than pro-<br />karyote-like."<br /><br />The url I gave for their joint paper is no longer valid, but the following url provides a link to a pdf file of the paper.<br /><br />http://scholar.google.com/citations?view_op=view_citation&hl=en&user=YrQEE_4AAAAJ&citation_for_view=YrQEE_4AAAAJ:d1gkVwhDpl0C<br /><br /><br />pnyikoshttps://www.blogger.com/profile/02592853123275492816noreply@blogger.comtag:blogger.com,1999:blog-1943438907128937267.post-4669859911942656462014-10-21T08:25:38.515-07:002014-10-21T08:25:38.515-07:00This comment has been removed by the author.pnyikoshttps://www.blogger.com/profile/02592853123275492816noreply@blogger.comtag:blogger.com,1999:blog-1943438907128937267.post-34621436393147288562013-10-15T08:06:52.059-07:002013-10-15T08:06:52.059-07:00Hunt misses out on a much less theoretical objecti...Hunt misses out on a much less theoretical objection Meyer had to the genetic code: that ribosomes, shorn of their sophisitcated proteins, are unable to produce polypeptides of appreciable length; branchings soon become inevitable.<br /><br />There are two weaknesses in Meyer's argument. One is that the rRNA component of the ribosome might have degenerated as a result of the addition of these dozens of accompanying proteins. The other is that Meyer nowhere takes advantage of the Achilles' heel of abiogenesis (of life as we know it): the protein takeover. <br /><br />There have been interesting and plausible speculative scenarios for the evolution of the genetic code that take us to the protein takeover. The best I have seen so far is a rather old one:<br /><br /> AM Poole, DC Jeffares, D Penney, The path from the RNA world. J.<br />Molecular Evolution 46: 1-17, 1998. <br />http://awcmee.massey.ac.nz/people/dpenny/pdf/Poole_et_al_1998.pdf<br /><br />But it stops at the threshold of the heart of the protein takeover, the replacement of almost all ribozymes by protein enzymes. I have never seen any attempt at a scenario for this, not even a highly speculative one. <br /><br />The most crucial for the genetic code (READ: the whole protein translation mechanism) is the advent of the highly diverse aa-tRNA synthetases. Their astonishing fidelity is presumably better than that of the hypothetical ribozymes they replaced, but we are in a catch-22 situation: as their conjectural precursors began aa-tRNA binding, they would perforce have had LESS fidelity than the ribozymes their "Darwinian" descendants ultimately replaced. And as such, they would be detrimental to the "fitness" of the cells in which they arose.<br />pnyikoshttps://www.blogger.com/profile/02592853123275492816noreply@blogger.com