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From: roy@phri.UUCP (Roy Smith)
Newsgroups: net.bio
Subject: Re: What's this LIFE stuff?
Message-ID: <2450@phri.UUCP>
Date: Fri, 10-Oct-86 12:33:11 EDT
Article-I.D.: phri.2450
Posted: Fri Oct 10 12:33:11 1986
Date-Received: Sun, 12-Oct-86 04:43:13 EDT
References: <7670@tekecs.UUCP> <812@hdsvx1.UUCP> <7706MIQ@PSUVMA>
Reply-To: roy@phri.UUCP (Roy Smith)
Organization: Public Health Research Inst. (NY, NY)
Lines: 33
Summary: alternates to DNA

In article <7706MIQ@PSUVMA> James D. Maloy writes:
> [...] could we bring DNA into the definition?  Is it possible
> (theoretically, anyway) for life to exist without it?

	If you are willing to concede that viruses are alive, then the
answer is yes.  There are viruses that use RNA as their genetic material
instead of DNA.  Of course, this is really sort of nit-picking.  RNA and
DNA are both nucleic acids that differ only in some fairly minor chemical
details (don't try telling that to a hard-core structure person, though).
As far as information storage goes, there is a trivial one-to-one mapping
between the two.

	I don't see why there is any reason why you can't have living
things without nucleic acid heteropolymers (i.e. DNA or RNA) being used for
genetic storage.  Of course, it wouldn't be life as we know it, but you
could speculate about auto-replicating polypeptides or polysacharides.
Both of these systems would maintain one of the basic properties of nucleic
acid base genetic material; you can store information by stringing together
strings of similar, but differentiable, building blocks.  All three types
of building blocks have consistant inter-block interfaces to simplify
polymer construction and various side-chains to provide information storage
and processing.  Sounds sort of like Ritchie's streams, doesn't it? :-)
There is no reason to believe that these systems exist, and to make them
work would require revamping most of the metabolism of the cell, but I
suppose they are possible.

	To go out on the speculative limb even further, do we even need to
store genetic information in heteropolymers at all?  I suppose not, but I
can't imagine how it would work.
-- 
Roy Smith, {allegra,philabs}!phri!roy
System Administrator, Public Health Research Institute
455 First Avenue, New York, NY 10016