I may have a plausible cause for the wobble in 3rd position and ask any good biochemist out there
to comment.
I don't think it was to get to a future 20 aa's. Instead I think it was the placement of the bases
then and their stability in their environment. Specifically I think the first anticodon was 3 bases
on the acceptor stem and that the 3rd one - the one out on the limb - started the wobble condition.
This was later mimiced in the 3 bases of the anticodon that we know on the tRNA today.
1. IF there was a connection between the aa and 3 bases in the acceptor stem (either directly or
through an enzyme) and
2. IF these 3 bases were 73, 74, and 75 (with #76 coming later perhaps or just too far out to fit.)
THEN they would mimic the anticodon.
In both cases the 2nd base or inside base of the 3 would be protected on both sides by other bases.
It would also be the strongest position if and when all 3 were h-bonded to other molecules.
The first base - #73 in the acceptor stem and #36 in the anticodon would both have bases next to
them and be in the 2nd most stable position. But the 3rd in both would be in precarious positions.
In #75 it is out on a limb so to speak and would be the weakest of the 3 bonds with only #76 beyond
it (and it may not have been there. In #34 it too would be in the weakest postion at the end of the
anticodon loop.
Therefore in both positions we have similar circumstances of h-bond fit. And in both cases the
outside base would be the weak wobble base, with the strongest position being the 2nd and the next
strongest the first position.
Also I would suggest that the acceptor stem 3-bases probably came first. And later the
anticodon followed.
Also it is likely that we now have at least 3 symbiotic conditions that would link both ends: temp
(hot or cold) pH (acid or base) and wet or dry.
Comment? Tom Hendricks