DNA Question

Mary K. Kuhner mkkuhner at kingman.genetics.washington.edu
Fri Dec 11 19:54:19 EST 1998


In article <74rhn7$hn4 at net.bio.net>,
John McKechnie  <J.M.McKechnie at ncl.ac.uk> wrote:

>Like language, which has a commonly agreed meaning among its users but no
>inherent meaning on it's own (I would be interested to hear serious
>objections to this), the relationships among species will account for common
>interpretations of DNA sequences. This does not change the fact that the DNA
>means nothing without something that 'knows' what to do with it.

I'm not sure that DNA is quite as arbitrary as language.  I've read
some science fiction (by Greg Egan) and some speculative non-fiction
(by Hofstader) which suggests arbitrarily rewriting the genetic code,
and re-engineering the whole mechanism of tRNA, amino acid transferase,
and so forth in order to accomodate the new code--you'd then, in theory,
have an organism with the same phenotype but a totally different
sequence of DNA.  However, I think we're seeing more and more evidence
that this wouldn't quite work, because the chemical properties of
a DNA sequence are important directly, not just as a transcriptional
template.  For example, if you rewrote all the coding regions in a new
code, any protein which used to interact physically with coding DNA
would stop working; any control mechanisms which depended on, say, the
GC content of the region might stop working; anything depending on
the details of coiling might stop working; anything depending on the
DNA or mRNA forming specific hairpin loops might stop working; anything
depending directly on RNA molecules acting as catalysts would certainly
break.

While an organism with a different code could certainly evolve de novo,
I don't think the current code is a cleanly separable subset of the
current organism.  There are senses in which DNA (or its RNA transcript)
*does* have inherent meaning, for example in its tendency to fold or
not.

Mary Kuhner mkkuhner at gnetics.washington.edu




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