Re: L- and R- amino acids

Raj (
Fri, 2 Feb 1996 18:37:14 +0000 (GMT)

Hello everyone,

As usual a mysterious "chiral force" was postulated to explain the
selection of one enantiomer over the other in chemical evolution (Pasteur
1860). Later considerations led to the idea that one chiral form took
over in evolution simply because:

1) it got replicating first
2) chemical interactions are stereospecific; resulting in selection of
the "first enantiomer" as the component of all living systems since.

I would be interested to know more about the claimed differences in
stability of L- and D- amino acids, it is difficult to think about any
reason for this when considering amino acids alone. Given that water is
not chiral, L- and D- amino acids should have the same stability in an
aqueos pre-biotic soup. But what if this soup contained inorganic solutes
of a chiral nature which catalyzed and determined chirality in subsequent
biological systems? In this case the initially random choice of chiral
precursor is pushed into the inorganic realm. Would geology and planetry
formation science provide clues?

It is true that the Yang-Mills (Yu ?) studies of the electro-weak force
established the existence of a chiral force in the universe (Nobel Prize
for Physics). Basically, when studying beta-decay (driven by the nuclear
weak force) from a cobalt-60 nucleus in a magnetic field (electromagnetic
force), they found that the direction in which the particles were emitted
did not reverse [as would have been predicted by the then accepted CPT
(charge-parity-time) conservation theory] upon reversal of the magnetic
field, but stayed the same (a very simplified explanation - see Martin
Gardener's "The Ambidextrous Universe" for a good explanation). The
universe has a clear preference for one direction (Left in our
convention) even if charge, parity or time are reversed. Among
other things, this broken symmetry in nature can be used to talk to
beings in other parts of the universe by radio to tell them our left and
right (who might also be made of antimatter (charge reversed) and tell
them not to visit us in case we all blow up. Conceivably,
civilisations evolving backwards in time could also be told about our
left from right, to help us fix up a meeting date.

But seriously, how do you tie a chiral force operating at the
subnuclear scale (10 the power -32 metres) to the molecular forces
operating at the nanometre scale?. This is the only way to explain
the selection of L-chirality in terms of the "universal chiral force".

If you know then expect an early morning phone call from Stockholm.

Get your brains round these:

1) Aliens land and are rushed away to a secret military establishment
(somewhere in New Mexico I think). Toe nail clippings collected by Dr
Ivno Grant stain blue with ninhydrin indicating a proteinaceous composition.

How Could Dr Grant determine if life on their planet was based on L-
or D- amino acids ?

2) Sam heats a piece of bread in his microwave because he is too lazy to
use the toaster. To his amazement, writing appears on his toast because
the microwave is picking up signals from a civilization about 10 light
years away.

"Greetings earthlings

We are an advanced civilisation made of the universal DNA, RNA and
Protein. Our hobbies are aerobics, keep-fit and stamp collecting. We are
looking for pen-friends. Please contact us on this frequency and you will
receive our reply in twenty years"

1) How would Sam find out if they are made from L- or D- amino acids?

2) Do you think Sam is on medication ?

3) Should he be ?