Non-nucleotide based life
Sandeep Pulla
earth, perhaps based on variants of nucleotides (sort of like the way
uracil replaces thymine in RNA), or perhaps based on completely
different molecules that have the "necessary" characteristics such as
the ability to polymerize & therefore store information, pair with
complementary molecules & self-replicate, and catalyze protein-like
molecules? I suppose the probability of such a thing happening would
be infinitesimal, but non-zero. Has any research been done on this?
Joachim Pimiskern
> Given sufficient time, can non-nucleotide-based "life"
> evolve on earth, perhaps based on variants of nucleotides
> (sort of like the way uracil replaces thymine in RNA),
> or perhaps based on completely different molecules that
> have the "necessary" characteristics such as the ability
> to polymerize & therefore store information, pair with
> complementary molecules & self-replicate, and catalyze
> protein-like molecules?
For example, there's tPNA as an alternative to DNA.
Some links:
http://www.iran-daily.com/1388/3424/html/science.htm
http://bill.srnr.arizona.edu/classes/182/EarlyEarth/BackTwoBases.htm
http://www.sciencedaily.com/releases/2002/12/021219065007.htm
http://nextbigfuture.com/2008/04/gna-glycerol-nucleic-acid-synthetic.html
http://thefutureofthings.com/news/1212/scientists-create-synthesized-dna.html
http://www.scienceblog.com/cms/fake-dna-used-build-nanotech-16152.html
http://www.scienceagogo.com/news/20060904023041data_trunc_sys.shtml
http://www.livescience.com/strangenews/090214-weird-life.html
http://rss.xinhuanet.com/newsc/english/2008-07/08/content_8510010.htm
http://www.newscientist.com/article/mg19926644.300-four-artificial-new-letters-for-the-dna-alphabet.html
http://www.thefreelibrary.com/Do-it-yourself:+virus+recreated+from+synthetic+DNA.+(Science+News...-a089815129
Regards,
Joachim
J.A. Legris
Aridaman Pandit
Hi Sandeep
A similar effort is underway by one of the leading scientist Dr.
Norman Packard, where he is using PNAs instead of DNA to mimic
formation of life from non-living chemicals. You can read it in detail
from the following link:
http://adi-38.bio.ib.usp.br/0440041/2006/NewScientistFeb05.pdf
It is really innovative and interesting effort. If you get to know
more of such projects do let me know.
Cheers,
Aridaman Pandit
Research Fellow
CCMB, Hyderabad
India
Alan Meyer
news:h1ola6$2cg$1...@darwin.ediacara.org...
If I interpret your question narrowly, the key phrase seems to me
to be "on earth". Given the restriction that we are talking
about earth, I suspect the answer to the question of whether new
forms of nucleotides might emerge is "No."
My arguments for this are as follows:
1. A new type of nucleotide, or life based on something other
than RNA and DNA, would require a great deal of supporting
chemical machinery, including the hundreds of enzymes need
for replication, transcription, repair, promotion and
suppression of gene expression, movement across membranes,
etc.
If the new nucleotides completely replaced old ones, then
we'd also need hundreds more chemical pathways for
managing the many other uses of nucleotides in the cell
besides gene encoding, such as in ADP/ATP, GDP/GTP,
AMP/cAMP, and other uses.
2. Any life form that evolved in the direction of the new
forms would have to compete against existing life forms
that already have highly developed biochemical machinery
for living based on the existing nucleotides.
The chance of succeeding in such competition seems to me
to be essentially zero.
3. Strong evidence for this view is found in the fact that
ALL known living organisms share the same RNA and DNA.
It's hard to believe that no other chemicals with similar
properties could exist, but if they ever appeared they
must have been destroyed by the existing forms.
Many people have asked the questions, Why isn't new life evolving
today? Why did life originate 3.8 or 4.2, or however many
billions of years ago but is not originating again now?
The best answer I have seen to those questions is that any
bioactive organic molecules that might serve as a basis for
evolution would simply be lunch for all of the existing bacteria
and other organisms out there. In the presence of existing,
highly evolved organisms, they would not have the time to undergo
the evolutionary process.
So too, I would expect any truly alternate biochemistry that
might begin to evolve on earth to have to pass through millions
or more of years of undisturbed evolution in order to get to a
successful, competitive state. But undisturbed evolution is no
longer possible. Competition is fierce.
Now having said that, I will postulate two possible ways that an
alternate biochemistry might appear anyway:
1. Perhaps there are extreme environments on earth where
currently known organisms cannot live but some different
kind of organism with a different biochemistry could live.
It might then evolve in the absence of competition.
We have found some really exotic biochemistries in extreme
environments such as archaebacteria that metabolize
hydrogen sulfide. Maybe there is something lurking in a
deep hole in the ocean floor, or in a volcano, or buried
under antarctic ice, that we've never seen, that has an
alternate nucleotide structure. If so, it's unlikely to
ever become "mainstream" unless a large part of the earth
changes to those extreme conditions.
2. Humans (or our successors), might create artificial
conditions in which new chemical pathways could survive
and thrive. However, whether this should be called
"evolution" is another question.
At any rate, those are my inexpert speculations.
Alan
Sandeep Pulla
Thanks to everyone who responded. Apparently this is an area of active
and quite fascinating research.
Sandeep Pulla
> If I interpret your question narrowly, the key phrase seems to me
Yes, I was particularly interested in that scenario, because while
it's entirely possible that the basic "principles" of what defines
life are the same in extra terrestrial conditions, it's also possible
that the principles themselves are vastly different in ways we're yet
to discover/imagine.
> The best answer I have seen to those questions is that any
> bioactive organic molecules that might serve as a basis for
> evolution would simply be lunch for all of the existing bacteria
> and other organisms out there. =A0In the presence of existing,
> highly evolved organisms, they would not have the time to undergo
> the evolutionary process.
Unless, I suppose, the alternate life forms were based on elements (or
molecules) that are largely useless to (or that cannot be easily
"fixed" by) existing life forms.
> At any rate, those are my inexpert speculations.
Nice analysis, actually.