Take a strand of RNA. I now suggest that there is a loop end
and a naked stem end. The loop end has 3 bases , like the
anticodon. The stem end ends with ATP that connects that
base to the amino acid.
Now instead of my old idea that thermal stability of h-bonds
determined the genetic code, I've got this new idea.
If dimers are on either the anticodon loop end or the other
RNA it is paired to, then it can't code because it can't
pair together. Thus isolating that molecule from attachment
to any other RNA
If there is coding such that the middle base is a pyrimidine
then neither the first or 3rd position can be pyrimidines
(that would be a dimer = 2 pyrimidines side by side on the
same strand - and remember even if there is no dimer on the
anticodon there would be on its codon or matching RNA
molecule - so it still couldn't code
pyr, pyr, pyr / or pyr pyr pur / or pur pyr pyr/ all would
be dimers and not code UNLESS they were formed only in water
or protected from UV in some other way.
We are left with only 2 codons that are safe from dimers:
pur,pyr,pur or pyr,pur,pyr.
But with wobble bases that would extend it a bit in the
favor of purines. Also prebiotic experiments produce much
more purines than pyrimidines and more easily.
So we end up with mostly purine codons (With a slim chance
that it is a pyrimidine codon but only if it is pur, pyr,
pur OR in water or under shelter of some sort
The key is mostly 2nd position - whether its purine or
pyrimidine
So its dimers (not thermal stability of 3 h-bonds) that
sets up coding
1. mostly purine
2. a few pyrimidine under certain environmental conditions.
Now for the other end. The acceptor stem end.
Would it be possible for an RNA strand with ATP sitting
where the A on the acceptor stem is now - to use its
phosphorus to join an amino acid to this stem like it
does today?
Comment?