X-Message-Number: 13752
Date: Sat, 20 May 2000 08:15:15 -0400
From: Thomas Donaldson <>
Subject: why biomolecules are hard, and more

Hi!

Here is why I think X-ray methods will not give us the structure of
biomolecules (in general --- certainly there are simple molecules for
which that will be true).

The main problem is that many biomolecules are tight associations of
atoms. Certainly they can be unwound into one or more long strings,
but normally they don't take that form. This is true of enzymes, and
of structural proteins --- both of which together take up a large 
class of molecules. This becomes especially difficult because H
can play a large role in the total structure, even though the main
bonds aren't between hydrogens but between other kinds of more visiable
atoms.

I especially don't mean here that we cannot find out the structure of
biomolecules. It's just that we'll want other evidence, too.

Finally, there is a CENTRAL ISSUE here which needs to be answered by
those who propose using X rays. No, it's not the issue of how their
use might destroy or affect many molecules. The fact is, a lot of
work has gone on up to now to find the structure of many biomolecules,
and that work will certainly continue. Yes. X-rays are used, but not
on single molecules but on collections of one kind, ideally crystals.
Moreover, the ability to COMPUTE structure is still increasing; one
major effort aims to produce a much larger parallel computer than 
even before (by IBM), with the result that even present methods will
be able to compute structure for much larger molecules.

This makes me think that the structure of biomolecules simply won't
be a problem we'll have to solve in trying to revive someone, even
if that person had been suspended with contemporary methods. The main
problem is likely to be that of recovering connections between neurons
even when some neurons have been destroyed. As for the damage of freezing,
it does not consist of production of new molecules so much as their
disarrangement. So chasing after means to work out the structure of
biomolecules merely repeats work which has been going on for 20 years
or more.

			Best and long long life to all,

				Thomas Donaldson

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