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From: lmc@denelcor.UUCP (Lyle McElhaney)
Newsgroups: net.misc,net.origins
Subject: Re: Time and the Amino Acid Motorcycle
Message-ID: <516@denelcor.UUCP>
Date: Tue, 24-Jul-84 22:24:06 EDT
Article-I.D.: denelcor.516
Posted: Tue Jul 24 22:24:06 1984
Date-Received: Fri, 27-Jul-84 01:47:18 EDT
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Organization: Denelcor, Aurora, CO
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I think I will try to show by example the mechanism by which chance is
*not* brought to bear in a chemical (or biochecmical) reaction.  I am
paraphrasing Isaac Asimov in the essays I cited in my previous article.

Let us examine the probability of assembling a water molecule from its
constituent parts.  A water molecule consists of an oxygen atom and two
hydrogen atoms.  If we simplify matters (I'll get into detail later), we
can see that there are a number of ways in which the atoms could possibly
unite to form *something*:

				       O - H
	H-O-H           O-H-H           \ /
	  2               2              H  2

All other combinations are congruent with these three.  The numbers are the
number of possible ways that the three components could combine to produce
that particular combination.  In each case there are two possible ways, so
using purely chance to define the ways in which these three molecules could
combine, there is a 1/3 chance for each.  This means (from a probabalistic
point of view) that each form is equally likely, and that if 300 atoms of
oxygen were combined with 600 hydrogen, there would be 100 molecules of
each produced.

Now, only one could be water; it is a tenet of physical chemistry that the
form of a molecule is at least as important as its constituents in
determining its properties.

How is it, then, that when a mole of (atomic) oxygen and two moles of
hydrogen are combined, we get exactly one mole of water?  By the numbers we
would expect 1/3 mole of water and 1/3 mole each of two other substances,
but multiple experiments have shown that this doesn't happen.

The reason is that the atoms have preferred modes of combining with other
atoms to make up molecules.  These are expressed in the structural notation
of biochemistry by the number of dashs which link a given atom to its
neighbors in schematic diagrams, like the ones I used above.  Oxygen, for
instance, has two such "bonds", while carbon has four and hydrogen one.
These bonding numbers cannot be violated unless great stress is applied,
and even then the molecules thus made generally break down when the force
is eased.  This being the case, it can be seen that there is in reality
only one possible combination, the first displayed above, and therefore all
H2O is indeed water.

Further complications arise from the fact that physical chemistry takes
place in three dimensions, and that the bonding counts are not the only
forces which compel molecules to form as they do. Water, for instance has
its two hydrogen atoms not exactly opposite each other, but rather they
form an obtuse angle with respect to the oxygen atom in the center. Many
of water's most interesting (and useful, not to say vital) characteristics
stem from the asymmetry thus produced. These complications only make the
du Nouey argument weaker, for rather than there being 3 possible combinations
of H2O there are in actuality an infinity of possibilities, only one of
which is really water.

Enough. Bring on some better arguments, or quit the ring.
-- 
		Lyle McElhaney
		(hao,brl-bmd,nbires,csu-cs,scgvaxd)!denelcor!lmc