On Wed, 19 Jan 2000, Damien Broderick wrote:
> At 08:33 PM 18/01/00 -0500, I wrote:
>
> >For a real world example -- ask yourself this -- If you have
> >three "molecules" and a genetic program for them, i.e. the DNA for
> >the genes of RNA and DNA polymerases and the ribosome subcomponents
> >and one of each of those"machines" to implement the cycle:
> > DNA -> RNA; RNA -> Protein; Protein makes more DNA & RNA
> >how fast can that system double itself (given unlimited energy
> >and material resources)? I haven't worked it out yet, but my
> >brief investigation into the limiting factors (rates of transcription)
> >suggests that it doubles in very short periods (probably minutes).
>
> I believe it's on the order of 15 minutes.
>
The fastest replication time for bacteria is 20 minutes. Given the
fact that it takes about an hour to copy the genome in E. coli this
rapid replication is a good trick (read "parallelism").
Given the E. coli genome is 4 Mbases, a 1 hour copying time works
out to 1000+ bases a second. Now I thought the fastest amplification
rates in PCR were around 50-100 bases/sec, so something seems strange
in these numbers. Perhaps the thermostable polymerases are much slower.
If we were just dealing with DNA copying and assumed you needed
only to copy 100,000 bases (DNA Pol+RNA Pol+Ribosome DNA), that
would allow a doubling time of 1.5 minutes. I believe the rate
limiting step is in the ribosome protein production, which has a
slower transcription rate than DNA or RNA polymerase.
This needs a lot more research since I want a really accurate number.
But it points out how fast self-replicating systems can be.
Bacteria could be considered to be "semi-optimized". In human
designed systems, since you can do "active" transport and run
the materials through an assembly line that requires minimal
tool motion/tip-changing and so the replication times are likely
to be much faster.
Robert
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