I'm looking at the orign of life. Specifically at the end that joins an amino acid (AA) to the tRNA
with an aaRS enzyme. And what I see is a zoo of weirdness and variation that would make sub atomic
particles look simple.
My question is this 'what came first and why?"
Here's the zoo between. It starts with the RNA strand of about 350 bases. The middle 85 bp (base
pairs) fold up into that cloverleaf pattern of tRNA we all have seen. Then along come enzymes to
clip off the excess bases. On the 5' end 41 bases are clipped - not too many but defintely shows
that the final bases are in the well protected center of a long strand. On the 3' end 225 bases are
cut - that is a lot of excess. Not only that but it leaves 3 bases beyond the acceptor stem with its
ACC coding. Now here is a curious part that interests me a lot. A special enzyme RNAse D (which
unlike the other 2, is exonuclease) has the job of cutting off just these 3 bp beyond ACC. Why just
3? Is this primordial?
Also the acceptor stem itself, the ACC, has an enzyme tRNA terminal transferease that can readily
remove and add this sequence to tRNA's that possess it or add it to tRNAs in which the sequence is
not present in the original gene.
Further complication arises with the aaRS or enzyme that joins the AA to the tRNA. It first joins
the aa to the nucleotide a-phosphate to activate it. Then it attaches to the ribose. But here it can
join at the 2' end, the 3' end, the 2' and 3' end, or neither.
So now reader - what's the order of the above in history. Specifically what came first - what is
primordial - how did the first proto tRNA join with an AA and why - what was in it to allow each to
surivive longer together, than apart. Remember the eye analogy so often used in selection. If we are
to accept that nothing evolves full blown - then that is true here - and this zoo between has a long
line of chemical evolution. But what is it?
(And please excuse errors in my chem knowledge which is admittedly poor) Tom Hendricks