[extropy-chat] HISTORY: Solved & Unsolved Riddles

[Rafal Smigrodzki]

----- Original Message ----- 
From: "Robert J. Bradbury" <bradbury at aeiveos.com>

>
> > 3. Why is all life on earth asymmetric at a molecular level. The amino
> > acids that make up proteins on earth all have a "left-handed"
> > (levorotary) chirality and the sugars that make up carbohydrates are
> > "right-handed" (dextrorotary). [snip]
>
> I believe this problem also has a "reasonable" proposed solution.
> I cannot recall it in detail but it has something to do with the
> interaction between light and dust in young stellar nebula.  Perhaps
> Amara might know the specifics -- otherwise I'd have to go digging
> for it.

### Probably no need to invoke the stellar dust, since the asymmetry is a
direct consequence of the mechanics of biological macromolecule synthesis.
An enzyme, ribosome or nucleic acid polymerase can recognize only a limited
number of molecular species (just like a lock can recognize only a limited
number of keys, all of the same general symmetry), and the moiety that forms
the most rigid part in a polymer, the backbone, can only assume a limited
number of conformations. Using a standard conformation for the backbone of
all monomers saves on the number of enzymes needed to make all the
components, and the standard conformation for aminoacids just happened to be
the L-conformation.

Of course, if there were any imbalances in the concentration of one
enantiomer in the primordial soup, that enantiomer would be much more likely
to become the standard, but, one way or another, a standard had to choose
itself.

Rafal