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I was reading a course about tolemers when I arrived to this phrase :

[...] The ends of a linear DNA molecule cannot be replicated by the cellular replication machinery (which may be one reason why bacterial DNA molecules are circular).

I want to know what is the relationship between the circular shape of the bacterial DNA and the blocking of replication machinery ?

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    $\begingroup$ What research have you done to answer this yourself? Please read the Wikipedia articles on telomeres and telomerase to understand what happens with linear chromosomes. You should also read about DNA replication in both prokaryotes and eukaryotes. Homework questions are off-topic on Biology unless you have shown your attempt at an answer. For more information see our homework policy. $\endgroup$ – MattDMo Nov 28 '16 at 15:13
  • $\begingroup$ It’s not a homework question, it’s a question out of curiosity, I’m trying to understand an idea proposed by Liz Parrish to reverse aging by adding some portions of telomers to the human DNA, so I want to know, how the shape of the bacterial DNA makes the bacteria immortal (if I can say so). $\endgroup$ – Bilal Nov 28 '16 at 15:26
  • $\begingroup$ Prior research is still required, regardless of whether the question is an academic assignment or not. Additionally, please edit your question to add and expand upon what you just put in your comment, as it makes the scope of your question completely different than what you originally asked. Remember, you need to include as much information as possible in order to get the answer you're looking for. Include what research you have done, what you understand so far, and where exactly you're stuck. $\endgroup$ – MattDMo Nov 28 '16 at 15:40
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This has been covered elsewhere (I highly recommend this page ) but it basically has to do with the priming of the strands and the fact that all polymerases work from the 5' prime to the the 3'. I made a quick schematic to illustrate (the explanation is below):

Schematic of DNA replication

The priming is done with RNA during DNA replication in the cell, unlike PCR where you use DNA oligo's to prime. This RNA-DNA is called the Ozakazi fragments. After replication RNAse H will remove these primers leaving only DNA's and gaps. In the middle of the sequence the gaps can be filled in by the normal repair machinery but at the ends there is no 3' terminus to fill in the gaps. That is where the telomerase comes in and fill these gaps with a fixed sequence (also based on an RNA template but that is going into details). If you have a circular chromosome there is always a 3' to complete the gap.

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