Re: UV Absorbance difference between Purines and Pyrimidines

On Sep 24, 12:18=A0pm, Alan Meyer <amey...@xxxxxxxxx> wrote:
Tom Hendricks wrote:
...
What if UV is a selective force at the start of life. If

=A0> purines, and pyrimidines have slightly different absorbance
=A0> maximums, then wouldn't each have a selective advantage
=A0> under certain UV conditions?

I think the answer to this question is an unequivocal No, at least
for DNA based life forms.

Every DNA base pair contains exactly one purine and one pyrimidine.
If UV light were deleterious to either one of them it would
have the same negative effect on DNA, destroying the same set of
base pairs.

=A0 =A0 =A0Alan

But at the start of life we had a strand of RNA. What if the UV was
such
that it was most dangerous to purines? Then we would have an
RNA pyrimidine world. Or depending on how the RNA folded, there
would be vulnerable purines at the ends so damaged by UV that they
could not fold
or react properly.
Look at a tRNA. I think you'll see a structure that is in many ways a
response to
UV. Think of pyrimidine dimers and how that could effect the origin
and coding.

If purines and pyrimidines both have differences
two hydrogen bonds versus three
different UV absorbance
then that must account for some selection differences.

.

Relevant Pages

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    ... What if UV is a selective force at the start of life. ... purines, and pyrimidines have slightly different absorbance ...
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