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BIO question on Kaplan

Discussion in 'DAT Discussions' started by pandalove89, Aug 6, 2011.

  1. pandalove89

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    The DNA of a bacteria is labeled with a radioactive phosphate. Following mitosis, each daughter cell will have:

    A. 1/4 the radioactivity of the parent
    B. 1/2 the radioactivity of the parent
    C. The same radioactivity as the parent
    D. 2 times the radioactivity as the parent
    E. It is not possible to determine

    I was stuck on either choice B and C, but I chose C and got it wrong.

    The right answer is B, and their explanation is something to do with semiconservative replication which I understand, but don't bacteria use asexual reproduction and therefore have the exact DNA structure of their parent?
     
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  3. PooyaH

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    It is asexual reproduction but what you're missing is that before the bacteria cell split into 2 daughter cells, it has to go through replication first. And as you mentioned replication of bacteria could be semiconservative, therefore each daughter cell would have only 1/2 of the radioactivity of the 'mother' bacteria. Meaning, the double strand DNA of each daughter cell contains 1 strand of the labeled DNA and 1 strand of newly synthesized DNA (via replication).
     
  4. pandalove89

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    but if it's asexual then where would the other "daughter" strand come from? There's only one "parent" in this case
     
  5. newbie1990

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    i thought bacteria only reproduce through binary fission? what pooyah is saying makes sense if it was mitosis, but bacteria don't have a nucleus - how do they do mitosis? and bacteria have a single circular strand of DNA... the idea of being semi-conservative shouldn't have to do with anything...

    confused... anyone else?
     
    #4 newbie1990, Aug 6, 2011
    Last edited: Aug 6, 2011
  6. LetsGo2DSchool

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    Ignore the wording of "mitosis" in the question. It's a typo. They're really asking: after replication, how much of the daughter DNA (btw, why can't it be a son???) is composed of the original DNA?

    The answer would be 1/2. If the original DNA strands were A1A2, then the daughter DNA strands would be A1B1 and A2B2. Thus each one is 1/2 new DNA and 1/2 original DNA.

    Btw, bacteria is double stranded. If you a google image search on 'bacteria dna replication' you'll see what I mean in the third photo.
     
  7. newbie1990

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    ahh... my bad, it is double stranded. confused "single circular dna" with single stranded circular dna. thanks.

    and, i'm fine with it being a daughter... ;)
     

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