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.
Let's see what has been 'proven' here. That if you manipulate chemicals in the laboratory you can get an enzyme out of two chemical bases - one of which is not one of the bases on which all life is based. Now this research does not tell us where they got the RNA strand, but I am sure that they 'borrowed' it. Of course, they created an enxyme which they refuse to name and may not even occur in any living thing. Of course even if you get an enzyme you will not get a living thing. You need the whole structure of some half million DNA bases and you certainly cannot have a working living thing with only two DNA bases one of which does not appear in any living thing. There are also lots of questions as to how the transcription took place and how much intervention was necessary to accomplish it - the article does not bother to say that either. You certainly need the cell itself for a living organism because the transcription needs material to form the enzyme, protein, or whatever it is producing. The so called scientists that did this so called research also did not even try to simulate natural conditions. They were trying to prove a point and used all the scientific knowledge we have to try to prove it and ended up proving nothing. Another example of our tax dollars at work!
Sorry, we already anticipated your call for a 300 million year experiment in a posting above.
Well, you just wait until a tornado rips through your junk yard.
I guess this just demonstrates what you know about DNA and molecular biology.
Unless you are asserting DNA structures are formed and controlled by magic rather than electron configurations, then it's not clear what your objection is.
The point is that just as snowflakes can acquire complex and macroscale structures without an "intelligent designer" so too can other chemical structures arise.
Since we know DNA exists, you have a long haul to prove impossibility of natural events. Begin.
Coming from you that's like a certificate of sanity!
The linear sequence of bases in DNA is not determined by the chemical bonds. That is why it can code.
|
All of those sequences are allowed and apparently in any order and number. Try to code with ice.
Ha ha ha ha ha ha ha ha. Talk about straining at a gnat and swallowing a camel! The research simply shows that one can synthesize an enzyme using a nucleotide constructed of only two bases. All the rest is hand-waving.
They fear that their well-settled worldview may require some re-thinking, and that's something they're so ill-equipped to do that it terrifies them.
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.