Pions and Life
Name: Sidd H.
I read your question about the smallest organism, and I
was wondering if Prions, single protein pathogens, could be counted as
organisms since viruses are. This would make them the smallest organism,
Scientists still argue over whether viruses ARE organisms. I wouldn't count
prions as organisms, but I would say they are the smallest INFECTIOUS AGENTS.
If you would take reproduction as the main criteria
for being a living organism, then prions fit that
criteria: they reproduce themselves by forcing
pre-existing proteins to become like them. Prions are
mammalian proteins that are folded in a particular
way: In this structural shape they are (1) extremely
stable, (2) disabled in their normal action in
cellular life and (3) can force normally folded
proteins of their kind to fold into this prion type.
However, reproduction in this way is different from
classical biological reproduction in that it can only
produce 'offspring' from already existing akind. And
there is no nucleic acid involved in their life cycle.
That is the major distinction with viruses.
I had a discussion with a geologist once who described
how chrystals are produced from minerals dissolved in
fluids. They form to a regular shape and pattern, and
the way chrystals grow is similar to biological growth
in some respect. Still, we would not call chrystals
living material. I think the growth of prions belong
to this same class of materials, although they are
produced from organic material.
Whether or not you would include prions as independent
living organisms depends on what definition you want
to accept. They are certainly infectious, and
pathogenic, and their discovery forced us to
reevaluate our views on infectious diseases.
Nope! Neither prions nore viruses are considered organisms...if one
considers an organism a life form.
Click here to return to the Molecular Biology Archives
Update: June 2012