On Thu, 26 Feb 2004 06:37:39 +0000 (UTC), tomhendricks474{at}cs.com
(TomHendricks474) wrote:

>"Without noncovalent bonds, such vital life activities as
metabolic reactions,
>duplication of DNA, and movement of materials within cells could not occur."
>Cell and Mole Bio, Karp
>
>Knowing how key noncovalent bonds are to every aspect of life
>how could it begin with covalent bonds instead?
>Doesn't it make sense that the origin of life was variants of
>noncovalent bonds?
>
>And just a side note. To get variants to select from, you
>would have to have variant conditions in the environment -
>correct?
>The alternative of never changing conditions would NOT
>produce variants.
>
>Thus to get variants you would have to have an environment
>with variatable conditions - a heat cycle.
>
The world of chemistry includes a whole range of chemical bonds:
ionic, covalent, and a whole series of weaker interactions.  All of
them play a role in living systems. They differ greatly in their bond
strength.  The dynamics of life requires some parts -- structural
components -- to have bonds extremely stable to thermal agitation (kT
or RT levels of energy).  Other aspects are quite variable and require
smaller energies so that changes are possible -- conformation changes
in proteins, for example, or temporary binding of ligands to
receptors. All the different bond types, ionic, covalent, and weaker
hydrogen bonding and the like play a vital role in cell processes.

I don't understand the need to say "life began with covalent bonds" or
"life began with non-covalent".  Wouldn't it be better to simply
assume that "life began with a suitable combination of a variety of
complex chemicals combining ionic, covalent, and other forms of bonds
to allow relatively stable structures to interact in a complex
dynamical system"?

And the note of variation also doesn't make much sense.  Variation
originates in mutation -- inaccuracies in a copying mechanism so that
offspring are not all identical to the parent or to each other
(without regard to whether the reproducing objects are molecules or
organisms or systems).  It is not caused by variation in the
environment.  In addition, you don't need a "heat cycle" to produce
environmental change. Spatial variation will do.
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