DNA Replication Rates lower Eukaryotes and Prokaryotes... why a difference...
dellaire at ATLAS.ODYSSEE.NET
Tue Jan 16 01:05:18 EST 1996
>for a biology paper,=20
>i need to solve the follwing question:
>WHY IS DNA REPLICATION IN PROKARYOTES NEARLY 100 TIMES FASTER THAN
>REPLICATION IN EUKARYOTES ?
The numbers I have quote:
E.coli at 500 nt/s and Human Fibroblast at 50 nt/s
that would be 10X faster
>i have wondered if it is because of (a) life span of pro vs eu
>karyotes, (b) because of existence ofa nuclear membrane in eukaryotes,
>where one is not found in prokaryotes...
>if anyone can shed some light on this question, please reply by
>posting or send email to:
k.venkiteswaran at odyssey.on.ca
Here are a few possibilities I could come up with.
One, in E.coli you are not worrying about mutations that much.
In fact =
a high mutation rate is desirable if the bacterium is to adapt
changing environments. The result is you can replicate your DNA
without worrying about a mutation occurring. In higher
eukaryotes such =
as mammals this is a big problem... mutations can kill the
organism if well placed (i.e. cancer). For yeast I don't think
this is =
as strong a point as they are unicellular and much like in
--high mutation rates are adaptive.
The error rate in E.coli is consequently ~10-8 where as in
Fibroblasts it is ~10-10
Two in E.coli you have very little packing of DNA compared to
eukaryotes. To start DNA replication you need to gain access to
the DNA =
and expose the template for the polymerase. For instance you
have the =
HU protein of bacteria compared to H1, H2A, H2B, H3 and H4 as
well as =
the HMG proteins in mammals. The bacterial genome is much less
so by simple logic to replicate DNA it is much easier to gain
accesss to =
DNA in bacteria then in a mammal and hence it is faster in
Further as a point of interest
In E.Coli you only have one origin of replication where as in
cells it is estimated there are between 10 to the 4 --10 to the
possible origins. This may reflects both the difference in size
complexity of the two genomes as well as the speed at which DNA
replicated. Multiple initiations of replication could help
increase the =
time to replicate the genome if it is very large.
E.Coli has 3 X10 to the 6 bp and in the human genome there are
~3X 10 to =
the 9 or=20
1000X more DNA to replicate. =20
1000 X 10 (the difference in speed of DNA replication)=3D 10
000 or 10 =
to the 4
hmmmm by a rough calculation it makes sense why you have ~10 to
the 4 =
origins in the human genome and only 1 in bacteria.
To your suggestion of the nuclear membrane as a possible reason
higher replication rates I think the membrane provides a way of
segregating transcription and translation first of all and may
really have much to do with replication on a surface level. =20
dellaire at odyssee.net
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