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    Working with Plasmids: Linking, Twisting, and Writhing

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    An Escherichia coli plasmid in a closed circle with 5, 200 bp and naturally has 26 negative super coil turns.
    1.Calculate the linking number for this plasmid. Assume it is adopting 10.4 bps/turn of the regular B-DNA.
    2.The above super coiled plasmid has been linearized by treating with a dsDNA breaking enzyme. What's the length of this linear form of plasmid?
    3.What will be the linking number, twisting number, and writhing number of that linear form DNA?
    4.What are the changes of the linking number after each reaction of Topoisomerase I and Topoisomerase II?

    © BrainMass Inc. brainmass.com October 10, 2019, 2:49 am ad1c9bdddf
    https://brainmass.com/biology/dna-chromosomes-and-genomes/working-plasmids-linking-twisting-writhing-395635

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    An Escherichia coli plasmid in a closed circle with 5, 200 bp and naturally has 26 negative super coil turns.
    1. Calculate the linking number for this plasmid. Assume it is adopting 10.4 bps/turn of the regular B-DNA.
    Lk=T+W
    T=bp/10.4
    W= -26
    =5200/10.4 + -26
    Linking number = ...

    Solution Summary

    In this solution several questions regarding the supercoiling of an E coli plasmid are considered. Special attention is given to showing the linking, twisting, and writhing numbers. Also, changes introduced by topoisomerase enzymes are considered.

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