In article <277u9i$a3s at apakabar.cc.columbia.edu> jhj4 at namaste.cc.columbia.edu (Jeffrey Hall Jennings) writes:
>1st, as the subject alludes, I don't know what the command is to delete a character in EMAC (the default editor that appears when one uses rn.
>Anyway, my question is regarding DNA repair enymes that prevent uncontrolled growth of a cell by changing the bases to the original base. How could these
>enzymes have evolved? Wouldn't the cell that has mutated to have uncontroled
>growth be selected for? I can't think of a scenrio where these repair enzymes
>could be selected for.
>oo
>o
>g
>Woiul
>systems that
>ana
It is true that most DNA polymerases (those being the enzymes that, among
other, things repair DNA) are highly conserved, i.e. they have evolved very
early.
It is also true that speed of growth is a strong selective advantage on
single-celled organisms.
One should, however, note that single-celled organisms don't have such
thing as "uncontrolled growth". They grow as fast as they can, and speed of
growth is, as stated, selected for. As replication of the genome takes a
major part of the resources needed for cell replication, the size of the
genome is also a selective treat.
With genomes optimised for small size, most metabolic pathways in microbes
don't have "fall-back systems". Therefore it is of utmost importance that
there is no errors in DNA replication.
Enzymes for detecting and correcting replication errors are thus strongly
selected for. "Uncontrolled growth" became an issue only when multi-celled
organisms evolved, but by that time there already was a mechanism for DNA
rapair. This mechanism is preserved, as it is naturally a selective
advantage for multi-celled organisms, too.
Hope this answered the question.
Ari-Matti Saren
saren at operoni.helsinki.fi
