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KVPY Sample Paper KVPY Stream-SX Model Paper-18

  • question_answer
    E.coli has a circular DNA consisting of \[4.3\times {{10}^{6}}bp.\] There are 10 bp of DNA for each complete \[360{}^\circ \] turn of the double helix. Replication starts at one location in the genome and proceeds in both directions that is, there are two replication forks that move away from the origin of replication in opposite directions meeting when each has moved halfway around the genome. Under one particular set of growth conditions, 800 bp of DNA are formed per second at each replication fork. At how many revolutions per minute (rpm) is each replication fork rotating during replication?

    A) \[4800\text{ }rpm\]

    B) 800 rpm

    C) 9600 rpm

    D) 8 rpm

    Correct Answer: A

    Solution :

    Length of DNA\[~=4.3\times {{10}^{6}}bp\]Number of basepairs per one complete \[360{}^\circ \]turn of double helix = 10 bp Number of basepairs of DNA formed at each replication fork = 800 bp per second "Number of complete \[360{}^\circ \]turn of double
    helix formed at each replication fork = \[\frac{800}{10}\]
    = 80 revolutions per second
    = 80 \[\times \]60 revolutions per minute
    = 4800 revolutions per minute


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