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From: Bob Casanova <nospam@buzz.off>
Newsgroups: talk.origins
Subject: Re: origin of biological chirality?
Date: Sun, 18 Aug 2024 21:48:07 -0700
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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
>
>https://en.wikipedia.org/wiki/Spock_Must_Die!
>
>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".
>
>
-- 

Bob C.

"The most exciting phrase to hear in science,
 the one that heralds new discoveries, is not
 'Eureka!' but 'That's funny...'"

- Isaac Asimov