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 Posted: Thu Nov 20, 2003 1:49 am Post subject: The Zoo Between |
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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 |
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