How do others feel about dimers as being a key to
>the development of the genetic code from this
>and the numerous other posts exploring this
>possibility?
>
WLH
 I don't like it and from the lack of response apparently others may
not either. 

TH
I can't argue there.

WLH
It may not be possible to really talk from out different
timelines about the reasons. You see the development of the genetic
code occurring early before dimer repair mechanisms exist and I see it
coming late in the RNA world when mismatch strand repair mechanisms
(including recognizing a dimer mismatch) would have been used.

TH
I welcome hearing more about your timeline. Mostly I would like to hear about
the earliest part.
I'm skeptical that the RNA world and protein can
be developed separately and later brought together.
I think that idea has set up an impasse for OOL scenarios.

UV is the 600 pound gorilla in the OOL  and  I think
most scenarios choose to suggest there was enough
fluke room to get around it. I don't think so.
It and the sun and the heat cycle; are important in other aspects of the
process, so why would it not be a major factor. How can any part of this OOL
process escape it
for enough time to develop complicated ways to protect from it?

I left my last scenario - h-bonds as being the key -
because it just was too iffy and too much fluke and not enough bulk to it.

But the dimer scenario has legs for me. I think uv would have favored a purine
type world and a hydrophilic world, and for no other reason than that ,the two
were favored, they were bound together.

Later a UV free world (maybe a water world only) added pyrimidines/phobic in
some way. 

One post from a newsgroup points out something I didn't think of:
"Cyanobacteria are pretty UV tolerant. 
This is interesting since it suggests that earth's first
photo synthetic organisms were also. They had to be to some extent.
They had to get enough sunlight to photosynthesize, and this would expose them
to some UV. Seawater is more UV transparent than most people think. See... "UV
Radiation in the Sea" Jenlov, Nature.  - post by Robert Parson.

All in all there is so short a time for the origin, and so
much has to develop and so much of it must have developed at the same time,
that I don't see it partialling
out in a latter period as you do. I just don't see how the process could be put
on hold till the genetic code got
its dimer repar mechanism going. That's just too much
iffy stuff for me.

The dimer clues that I suggest, seem to bring things
together and  at an earlier time than most strung on scenarios.
It also gives a reason for a philic/phobic geared code.
It also gives a process - the sun made them and that energy was always there -
it wasn't a developed 
metabolism, it was a forced one, that forced a type of chemical adaptation.

WLH
 I'll just mention a couple things from earlier posts that caught my
attention.
 (1) You talk of how dimers might help explain wobble in the 3rd
codon/1st anti-codon position pairing and give some reasons. This
struck me as a very backward way to see a problem. By now you know
that looking at random rna strands and how they might bind in
mini-helixes you expect to see wobble. G=U pairings contribute as much
energy as an A=U pairing to these short helix formations. In the
ribosome, 100's of random tRNAs try to bind with a codon on an mRNA
before one is successful. The problem that requires explanation is NOT
why  wobble is observed in one position but rather why there is no
wobble in the other two? The current incomplete explanation is that
this not just a dance between codon and tRNA but the ribosome has its
h-bonding fingers in there also.
 (2) In another you mention I(Inosine) as a replacement for A as if it
may have been used in the tRNAs(1st anti-codon position) from some
early time. Inosine is essentially only used by eukaryotes and is most
certainly a replacement for the G which is used in eubacteria. A is
just not used. Likely this transition from G to I in eukaryotes
occurred only after the genetic code was "frozen". I(Inosine) in a
tRNA is not something that would be found while the genetic code was
still forming and in its early stages (meaning not present in the
timeline you use).
 William L Hunt  

TH
Both of your points seem valid. But even so they
just challenge the weakest points of my dimer ideas.
I would hope others will give my scenario another look.
It seems to answer most of the tough questions
for me - 

In the meantime I'd like to take a look at your ideas for
that timeline.

Tom

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