On Thu, 15 Aug 1996 18:13:32 -0400 (EDT), lhaarsma@OPAL.TUFTS.EDU wrote:
LH>These might interest this group:
>
>_Nature 382_ n.6589, July 25, page 373:
>"RNA-catalysed RNA polymerization using nucleoside triphosphates."
>A sentence from the abstract reads, "We describe here an RNA that synthesizes
>RNA using the same reaction as that employed by protein enzymes that catalyse
>RNA polymerization." The article was too technical for me to get much
>out of it; if anyone else understands it I'd appreciate a summary.
>
>_Nature 382_ n.6591, August 8, page 525:
>"A self-replicating peptide"
>The title is a bit of an overstatement. The authors found a 32-amino-acid
>peptide which catalyses its own synthesis from a neutral, dilute solution
>of 15- and 17-amino-acid fragments. (There's a non-technical summary and
>"perspective" piece by Stuart Kauffman on page 496.)
>
>Nice work, good articles.
>
>(No doubt these have already been used on talk.origins to support both
>the claim that abiogenesis is inevitable, and the claim that abiogenesis
>is impossible.)
This is was written up in New Scientist recently:
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Are proteins real key to life?
Philip Cohen, San Francisco
---PROTEINS perform most of the chemical tricks that make life as we know it possible-with one important exception. They do not hold the blueprint for their own replication. That important information is stored in genes. But now chemists in the US have built a protein that can replicate unaided. Their result is the first hard evidence that life could have arisen purely from proteins.
Many biologists believe that life began when a self-replicating molecule emerged on the primeval Earth and began to evolve. But determining which type of molecule started it all off has always seemed to be a chicken-and-egg problem. In all cells, the nucleic acid DNA stores genetic information, which is then copied into RNA and used to make proteins. Proteins, in turn, act as catalysts in gene replication. Thus, life appears to rely equally on three types of molecule.
But in the 1980s, Tom Cech at the University of Colorado at Boulder and Sydney Altman at Yale University showed that RNA could also catalyse chemical reactions. And many scientists then proclaimed that RNA was most likely to have been the molecule-of-all-trades at the dawn of life. This theory now dominates textbook explanations of how life began.
However, in the eyes of Reza Ghadiri, a chemist at the Scripps Research Institute in La Jolla, California, the case was never closed. "As far as we know it, proteins are the best catalysts on Earth, and I saw no reason why they shouldn't be able to self-replicate." The only thing that put natural proteins at a disadvantage when compared with RNA was that they did not act as templates for their own replications.
To test the idea, his team split GCN4 molecules into their identical halves, which they chopped into two chunks. They then mixed these at room temperature to see if they would join up again. Because there was no full-sized template around, the only way the fragments could do this was to find each other and link up by random motion. For that reason, the complete 32-amino-acid molecule reformed only slowly at first. But as the team reports in this week's issue of Nature (vol 382, p 525), the reaction got faster as it went on. "The only way that can happen is if the product was helping its own synthesis," says Ghadiri.
His explanation is that once the first full-sized protein piece was created, it acted as a template to accelerate the creation of the next. This pair then fell apart and each piece acted as a template for the next generation, and so on.
Gerald Joyce, a biochemist who studies test-tube models of the RNA world at Scripps, says: "It's just beautiful work, people literally gasp when he talks about it." But he adds: "I wouldn't say it shows life started with peptides." The problem, says Joyce, is that while every piece of RNA can serve as a template, the type of protein templating that Ghadiri observes may be a rare phenomenon unlikely to arise without a chemist's nurturing. Ghadiri disagrees. "I don't believe I'm that lucky. How could I have picked the one peptide in a million that can replicate?"
(Cohen P., "Are proteins real key to life?", New Scientist, Vol 151, No. 2042, 10 August 1996, p16)
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Note that although Ghadiri claims that he wasn't "that lucky" to have "picked the one peptide in a million that can replicate", it is clear that he selected a molecule that could be split exactly into two "identical halves" an then they did just that. They then gave it a "solution of 15- and 17-amino-acid fragments" from which it could readily build copies of itself.
While interesting and proof that at least one protein can replicate itself, is it really relevant to anything that would occur on the early Earth/Mars?
There is another problem with such protein replication: it is too exact. If no errors occur, then there can be no natural selection and hence no evolution, for example, in the case of an artifical protein:
"In the summer of 1990, Julius Rebek Jr., chemist at MIT, created astir by announcing that he had created a synthetic organic moleculethat could replicate itself The molecule, called amino adenosinetriacid ester (AATE), consists of two components that resembleprotein and nucleic acid. When placed in chloroform stocked withcomponents, AATE can serve as a template for the formation of newAATE molecules. G.Joyce, an RNA specialist at the Scripps Clinic,commented in Scientific American on Rebek's work: "They [MTE] onlyreplicate in highly artificial, unnatural conditions, and even moreimportantly, they reproduce too accurately. Without mutations, themolecules cannot evolve in the Darwinian sense." (Bradley W.L. &Thaxton C.B., "Information & the Origin of Life", in Moreland J.P.ed., "The Creation Hypothesis", InterVarsity Press: Downers Grove:Ill., 1994 p192)
The protein-first theory has always been rejected because proteins are too accurate:
"The conceptual bankruptcy of Oparin's "soup theory" was highlightedin debate held at the international ISSOL symposium in Berkeley,California, in 1986. The "protein-first" side of the debate arguedthat making RNA under prebiotic conditions was well-nigh impossible,a criticism that was ignored rather than rebutted by the "RNA-first"side. The latter responded by insisting that proteins are too ineptto be the vehicle for the first living system, since they areinsufficiently versatile. With the protein-first side providing norebuttal to this criticism, the debate ended with both positionsfatally flawed and no more promising alternatives suggested."(Bradley W.L. & Thaxton C.B., "Information & the Origin of Life", inMoreland J.P. ed., "The Creation Hypothesis", InterVarsity Press:Downers Grove IL, 1994, p193)
Indeed Shapiro, an exponent of the "protein-first" theory, says that if this simple protein pairing scheme existed from the beginning, there would be no need to move to nucleic acid:
"If proteins could replicate directly, by some simple pairing scheme, there would have been no need for them to turn this function over to nucleic acids. Proteins store the same information more economically, using less material. For example, an average amino acid in a protein chain contains about 16 atoms. The same information, stored in three units of an RNA chain, requires about 100 atoms. In DNA, the identical information is kept in a complex of two chains and needs 200 atoms. This extra expenditure of material in storing the same information would be justified only if there was a corresponding increase in efficiency in moving to the more complex systems. We must presume that the earlier protein-based hereditary system was more cumbersome, and less elegant, than the present one." (Shapiro R., "Origins: A Skeptic's Guide to the Origin of Life", Summit Books: New York, 1986, p282-283)
Of course, if Darwinist blind-watchmaker evolution was really true,proteins should have `found' this super-efficient direct copyingscheme in the 3 billion years at their disposal. That they didn't is evidence for the restraining influence of an Intelligent Designer.
God bless.
Steve
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