Re: origin of biological chirality?

On 8/18/2024 11:48 PM, Bob Casanova wrote:

On Sun, 18 Aug 2024 21:11:53 -0600, the following appeared
in talk.origins, posted by Pro Plyd
<invalide@invalid.invalid>:
 

RonO wrote:

On 8/18/2024 12:01 PM, Bob Casanova wrote:

On Sun, 18 Aug 2024 00:08:49 +0100, the following appeared
in talk.origins, posted by Ernest Major

>
For chirality there is an equilibrium ratio between the mirror images. D
sugars have been known to exist in solution at higher concentrations
that L forms.  My guess is that L forms of amino acids are likely to
exist at higher concentrations in solution, but it doesn't matter.  The
chirality of life was set by the first enzymatic reactions used by life
to get started.  The use of L amino acids would have been set by the
first functional proteases that could produce peptide bonds or for the
RNA world scenario it would have been L amino acids that were probably
used to make the first nucleotides.  The active sites of the first
replicated enzymes would have set the chirality, and that chirality
would have been maintained due to subsequent enzymes would have to be
compatible for the ones that came before.  Only one form fits into the
active site of an enzyme that uses that amino acid or carbohydrate.
Enzymes have evolved to convert one form into the other because they
spontaneously change from D to L and if left to themselves you would get
a mix at a certain ratio in solution.

Quite some time ago I came across (borrowed?) an old
scifi Star Trek novel called "Spock Must Die". There's
even a wiki page for it
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https://en.wikipedia.org/wiki/Spock_Must_Die!
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Anyways, that bad ol transporter makes a second
Spock. This second Spock was the chiral opposite
of the original Spock and was basically starving
because the food had the wrong chirality. Cool
stuff for 1970. Moral of the story is that the
chirality preference is universal!
>

Check out the Roger Zelazny novel, "Doorways in the Sand".

I took a science fiction English class at Berkeley and one of the reads was Zelazny's "A Rose for Ecclesiastes".  One issue with the story was the unbelievable interbreeding with the Martians, but in my essay on the story I proposed that because of the Biblical reference that Zelazny meant it as evidence for a common creator of both Martians and Humans.
Ron Okimoto

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