Posted on 12/19/2002 5:57:50 AM PST by forsnax5
Two scientists at The Scripps Research Institute (TSRI), Research Associate John S. Reader, D.Phil, and Professor Gerald F. Joyce, M.D., Ph.D., both of the institute's Department of Molecular Biology, have succeeded in creating an enzyme based on a "binary" genetic code--one containing only two different subunits.
This research, described in the latest issue of the journal Nature, demonstrates that Darwinian evolution can occur in a genetic system with only two bases, and it also supports a theory in the field that an early form of life on earth may have been restricted to two bases.
"Nobody will ever top this because binary systems are the most reduced form of information processing," says Joyce. "Two different subunits are the absolute minimum number you need [for Darwinian evolution]."
Where protein enzymes are polymer strings made up of 20 building blocks (the amino acids), and RNA or DNA enzymes are made up of four different building blocks (the nucleotides), the world's first binary enzyme has but two different building blocks, based on the nucleotides A and U.
This enzyme is functionally equivalent to a "polymerase" molecule. Polymerases are ubiquitous in nature as the enzymes tasked with taking a "template" string of DNA or RNA bits and making copies of it.
Reader and Joyce's binary enzyme is able to join pieces of RNA that are composed of the same two nucleotide symbols. In the test tube, the binary string folds into an active three-dimensional structure and uses a portion of this string as a template. On the template, it "ligates," or joins subunits together, copying the template.
If the origins of life are a philosopher's dream, then they are also a historian's nightmare. There are no known "sources," no fossils, that show us what the very earliest life on earth looked like. The earliest fossils we have found are stromatolites--large clumps of single-celled bacteria that grew in abundance in the ancient world three and a half billion years ago in what is now western Australia.
But as simple as the bacteria that formed stromatolites are, they were almost certainly not the very first life forms. Since these bacteria were "evolved" enough to have formed metabolic processes, scientists generally assume that they were preceded by some simpler, precursor life form. But between biological nothingness and bacteria, what was there?
Far from being the subject of armchair philosophy or wild speculation, investigating the origins of life is an active area of research and of interest to many scientists who, like Reader and Joyce, approach the questions experimentally.
Since the fossil record may not show us how life began, what scientists can do is to determine, in a general way, how life-like attributes can emerge within complex chemical systems. The goal is not necessarily to answer how life did emerge in our early, chemical world, but to discover how life does emerge in any chemical world--to ask not just what happens in the past, but what happens in general.
The most important questions are: What is feasible? What chemical systems have the capacity to display signs of life? What is the blueprint for making life in the chemical sense?
One of the great advances in the last few decades has been the notion that at one time life was ruled by RNA-based life--an "RNA world" in which RNA enzymes were the chief catalytic molecules and RNA nucleotides were the building blocks that stored genetic information.
"It's pretty clear that there was a time when life was based on RNA," says Joyce, "not just because it's feasible that RNA can be a gene and an enzyme and can evolve, but because we really think it happened historically."
However, RNA is probably not the initial molecule of life, because one of the four RNA bases--"C"--is chemically unstable. It readily degrades into U, and may not have been abundant enough on early Earth for a four-base genetic system to have been feasible.
To address this, Nobel Laureate Francis Crick suggested almost 40 years ago that life may have started with two bases instead of four. Now Reader and Joyce have demonstrated that a two-base system is chemically feasible.
Several years ago, Joyce showed that RNA enzymes could be made using only three bases (A, U, and G, but lacking C). The "C minus" enzyme was still able to catalyze reactions, and this work paved the way for creating a two-base enzyme.
In the current study, Reader and Joyce first created a three-base enzyme (A, U, G) and then performed chemical manipulations to convert all the A to D (diaminopurine, a modified form of A) and biochemical manipulations to remove all the G. They were left with an enzyme based on a two-letter code (D and U).
Reader and Joyce insist that their study does not prove life started this way. It does, however, demonstrate that it is possible to have a genetic system of molecules capable of undergoing Darwinian evolution with only two distinct subunits.
The article, "A ribozyme composed of only two different nucleotides," was authored by John S. Reader and Gerald F. Joyce and appears in the December 19, 2002 issue of the journal Nature.
This work was supported by a grant from the National Aeronautics and Space Administration (NASA), the Skaggs Institute for Chemical Biology at The Scripps Research Institute, and through a postdoctoral fellowship from the NASA Specialized Center for Research and Training (NSCORT) in Exobiology.
Had I thought of that term, I think I would have removed two of those letters.
No offense, but evolutionists have the smug attitude of "ours is science while yours is no better than magic, suckers." Well there is some point to that. But if you wrap yourself in a cloak of science you should live by the rules of science, and they say that gaps in the evidence taint your conclusions and cast doubt on them until you fill them. You may not like that, but if you choose to ignore that part of the scientific method then you have abandoned it. As for the "creationoids", they dont have the same burden of proof since they readily acknowledge their worldview is based on faith which cannot be proved or disproved. When scientists take the same attitude, a new religion is founded. So it seems in case of evolution.
From Nature
Using just two bases, Reader and Joyce mimicked the R3 ligase ribozyme, a stretch of RNA that latches onto another RNA molecule. Part of the R3 ribozyme has a base sequence that matches that on its RNA target molecule. The researchers constructed this binding sequence and target from A and U bases alone. Then, for technical reasons, they replaced the A's with a non-natural base called diaminopurine (D). The resultant ribozyme can be copied without the need for G or C bases. Copying is a necessary part of the process of finding a two-letter mimic. The researchers then eliminated all of the G's that they could from the R3 molecule while still retaining some of its catalytic behaviour (it can manage without C's). All but three could go; if the researchers took any of those out, the molecule was no longer catalytic. To get further, the researchers abandoned rational design and turned to in vitro evolution. They replaced the remaining G's at random with U or D, while shuffling a few of the other U's and D's in the molecule. None of the products made this way is a particularly stunning catalyst. But they work. The best, containing just U and D, links to the RNA target 36,000 times faster than in the absence of any catalyst at all. In other words, a two-letter ribozyme is a lot better than nothing. D isn't too difficult to create from the kind of ingredients that were probably available on the early Earth, say Reader and Joyce. They also point out the advantage of an RNA-like molecule that contains no C: cytosine decomposes quite quickly if it gets warm. |
Actually, there is no way to prove that yesterday happened.
All true believers are followers of the Cargo Cult and the Prophet John Frum (Blessing Be Upon Him!), and they know that the Universe was created when it fell out of the cargo hatch of an R4D flying over the Solomon Islands!
Have you ever looked at a magnified view of a snowflake? Very organized (yet rather spontaneous) structure that repeats in small ways that grow into a larger structure.
Crystalization is very definately "chemical" in nature. It has structure, it has reproducibility (from the small scale to the large.) Yet we attribute no magic behind it, no purpose, no goal, no "reader", no "intelligent designer."
DNA and other life forms are really just an ongoing crystalization process, if you will.
Bull.
Thanks for the Biblical quote.
Kind of like claiming that New York city is just a sort of an exxagerated ant colony...
Real experts have noted that RNA and DNA are vastly beyond the level of complexity at which something could just sort of happen.
So, are these "real experts" claiming RNA and DNA didn't happen?
Or are they "experts" in believeing the scientific musings of ancient goat herders?
"At that moment, when the DNA/RNA system became understood, the debate between Evolutionists and Creationists should have come to a screeching halt
I.L. Cohen, Researcher and Mathematician
Member NY Academy of Sciences
Officer of the Archaeological Inst. of America
Darwin Was Wrong - A Study in Probabilities
New Research Publications, 1984, p. 4
I gather from reading that mathematicians as a group are less than fond of evolutionism. Something about dealing with logic on a regular basis...
Hmmm, yeah, sounds unanimous. heh heh
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