Re: origin of biological chirality?

On 19/08/2024 04:11, Pro Plyd wrote:

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!
 

That is probably based on Arthur C. Clarke's 1950 short story "Technical Error" (originally published as "The Reversed Man"). (There is also, judging by descriptions, a more tongue in cheek 1987 story by Isaac Asimov - "Left to Right".)
https://en.wikipedia.org/wiki/Technical_Error