A possible definition of life.

Ed Rybicki ed at MOLBIOL.UCT.AC.ZA
Fri Apr 25 03:32:43 EST 1997


>    So does any definition requiring that a living thing code for itself 
>    AND replicate itself.

> Well...I think this rules me out as a living thing.  After all, I
> can't replicate myself.  The best I can do is to work with another
> organism (my wife) and generate something completely different but
> somewhat similar (my kids).  Even then, my wife doesn't do the all the
> work.  Ribosomes and such do the work.  

Sorry, James - the reality just biting, is it?  Ever think that maybe 
- outside of the lab, that is - males and females TOGETHER 
constitute an organism?

> What really replicates here, me or my DNA (and my wife's)?  Does this
> definition make the DNA alive, but leave me as an unliving
> repository...like a copying machine?

Yup, sorry!

> Also, what does it mean to "code for itself"?  DNA is not a computer
> program.  The sequence does NOT code for an individual.  The
> "blueprints" must also include: DNA structure, RNA structure, cell
> environment (a very big deal), and more I'm sure.  As geeks we like to
> think of computer programs as the model for life...but I suggest that
> this is as much an illusion as the "world is a clock" metaphor of the
> 1700s.  

I am afraid that the entire assemblage of moelcules constituting you 
or your wife is specified by nuclear and mitochondrial DNA - and the 
primary sequence of proteins (specified by the DNA genes) determines 
their tertiary and quaternary structure (with some help from 
chaperonins).  And the entire assembalge is what results in an 
individual - the fact that it might come out differently given the 
same collection of molecules is beside the point; so might a protein 
(eg: prion protein) have more than one stable conformation. 

                     Ed Rybicki, PhD  
      Dept Microbiology     |   ed at molbiol.uct.ac.za   
   University of Cape Town  | rybicki at uctvms.uct.ac.za
   Private Bag, Rondebosch  |  phone: x27-21-650-3265
      7700, South Africa    |   fax: x27-21-689 7573
    WWW URL: http://www.uct.ac.za/microbiology/ed.html      
                                        
"Every year is getting shorter, never seem to find the time..."



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