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Total number of DNA molecules after environmental change

  1. Aug 25, 2014 #1
    1. Suppose DNA molecules of a Streptococcus bacterium contain a radioactive isotope [itex]N^{15}[/itex], if this bacterium is then put in an environment containing only [itex]N^{14}[/itex] and after 5 generations (DNA duplication), how many [itex]N^{15}[/itex] DNA molecules remain ?

    2. Relevant equations

    3. after 5 generations, it is [itex]2^{5+1}=64[/itex]. But then I become clueless as to how I can reason the eliminated DNAs as well as their remaining number. Oh nooo...Help please...
  2. jcsd
  3. Aug 25, 2014 #2


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    2017 Award

    Staff: Mentor

    I don't see why the total content of N15 should change at all. It just gets splitted and distributed over multiple bacteria.
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