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What is the difference between replication and to divide? My A level bio book says that it takes 20 min for E.coli to divide and in next page it's written that E.coli completes replication within 38min.

Moreover, there is a diagram (shown below) which contradicts as what I thought.

Please explain the difference between replication and division.

enter image description here

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    $\begingroup$ Your question is unclear. The diagram you show has nothing to do with replication time per se, but with the mechanism. It shows the Messelson-Stahl-Experiment. So please clean up your question and make clear, what your question is. $\endgroup$ – Chris♦ Jun 16 '16 at 7:09
  • $\begingroup$ This diagram shows that to divide frm 1st gen to 2nd gen it took 20 min but then i read "E coli completes the process of replication within 38 min, average rate of polymerisation being 2000bp per sec. " but then that dig says that it took Ecoli 20 min to divide... And that is my confusion.. Is replication nd to divide different $\endgroup$ – user24511 Jun 16 '16 at 7:16
  • $\begingroup$ Here, replication means DNA replication, while division means mitosis. $\endgroup$ – another 'Homo sapien' Jun 16 '16 at 7:25
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    $\begingroup$ There is no mitosis in prokaryotes. This term applies only to eukaryotes. Say simply "cell division". $\endgroup$ – user24284 Jun 16 '16 at 8:04
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I am unsure if I really understand the question. Are you wondering how the rate of DNA replication can be slower than the rate of cell division if every daughter cell needs a chromosome copy?

If so, keep in mind that prokaryotes have different origins of replication on their chromosome so that DNA replication can actually be parallelised. Cooper (1968) presents a mathematical model that is consistent with experimental findings and indicates that when the DNA replication step becomes limiting for cell division, E. coli switches to multiple replication forks, thus decreasing the net time needed for complete DNA replication.

According to that, it is no contradiction that DNA replication per se takes longer than cell division.

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Replication refers to DNA replication and division refers to the cell division. Yes it is true that, in E.coli replication can be slower than the division time. This is a well known problem in molecular genetics.

The bacterium copes up with this by having a partially replicated genome during the beginning of the "cell cycle". So there are actually two origins of replication when a new cycle starts. When the replication proceeds you have multiple forks (from the replicated origins). Because of these multiple forks (forks within forks), the replication time speeds up. See the figure below:

enter image description here
From Fossum et al. 2007

For more details see:

Fossum, Solveig, Elliott Crooke, and Kirsten Skarstad. "Organization of sister origins and replisomes during multifork DNA replication in Escherichia coli." The EMBO journal 26.21 (2007): 4514-4522.



The picture that you have shown is something totally different. As mentioned by Chris, the picture illustrates the Messelson-Stahl experiment to demonstrate the semiconservative nature of DNA replication. Do not confuse that with the above problem. As for the 40min shown from generation-1 to generation-2, in this picture, I feel that it is a misprint.

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