what is alive?

Ed Rybicki ed at MOLBIOL.UCT.AC.ZA
Fri Sep 13 07:35:48 EST 1996

> To:            mol-evol at net.bio.net
> From:          Mario Vaneechoutte <Mario.Vaneechoutte at rug.ac.be>
> Subject:       Re: what is alive?

> Mike O'Hara wrote: 
> > > Carrying on from the original question (are viruses alive) and looking at Mario Vaneechoutte's definition, how do people feel about 'alive' for the BSE agent. At this stage it looks to be a vari
> > 
> Ed Rybicki wrote:
> > For me, it's simple: it's not replicating; like fire, it is simply
> > propagating a chemical reaction which varies according to its
> > substrate; therefore, it is not alive.
> itself', prions are alive. It came as a surprise that something else
> than  DNA-RNA could replicate on its own and by a completely different
> mechanism...
> prions
> keep transforming normal proteins into prion proteins.

Yes...BUT by acting as a peculiar catalyst, NOT by replicating any 
other information than purely structural.  Think about it: is the 
action of a prion protein in transforming another "normal" protein 
into a prion protein, any different to an antibody forcing a peptide 
into a particular configuration in its binding site, or a catalyst 
(read: enzyme) binding to, and forcing conversion of, its substrate?  
In this case the binder and the bindee CAN be the same protein in 
terms of primary sequence, or closely related variants thereof; 
however, it merely makes for a special case of a broader phenomenon 
which is simply catalysis.  Which isn't life....
                     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      
    "Out here on the perimeter, there are no stars..."

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