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AAMC CBT 10 BS Question

AlphaMagnum

Full Member
Jul 14, 2011
40
0
  1. Pre-Medical
    The important details:

    Experiment 2:
    Synthesized gene sequences from two known hantaviruses were mixed with nucleic acid from patients' lung tissues but not with lung tissue from control subjects. Hybridization between nucleic acid strands occurs when they base-pair with each other. Hybridization occurred between the synthesized genes and nucleic acid from the patients' lung tissues.

    The question:

    "In Experiment 2, why did the synthetic hantavirus gene hybridize with nucleic acid from an infected lung?"

    A) They were identical in sequence to genes from the lung.
    B) They were complementary in sequence to genes from the lung.
    C) They were complementary in structure to the protein encoded RNA from the lung.
    D) They encoded an enzyme that bound to the nucleic acid from the lung.

    Now...my problem is that nucleic acid in the passage doesn't seem to be defined as either DNA or RNA, leading to my confusion.

    I eliminated options C and D out of hand and I understand why the correct response is B, but here's my logic:

    If the hantavirus gene is identical to a gene from the lung (we can take the lung gene to be from the sense strand of DNA), it will bind to both the antisense strand of DNA from the lung as well as the mRNA produced based on the sense strand.

    On the other hand, a hantavirus gene complementary to a lung gene can bind only to the sense strand of DNA.

    This led to my choosing option A. Clearly, when they said 'nucleic acid,' they meant only DNA, in which case binding to the sense strand of DNA is slightly more relevant than binding to the antisense strand, though that sort of logic implies that (A) is a possible option as well.

    Can anyone help me out here?
     
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    tn4596

    Full Member
    7+ Year Member
    Jul 23, 2011
    848
    11
    1. Medical Student
      Oh, ok that clear up a lot. This is a very simple question and you got it wrong because you were overthinking it.
      All they are asking you is that: why did the two strand of DNA/RNA (doent matter which one it is) bind to each other?
      the right answer is that they are complementary. if they are identical they wouldnt be able to bind.
      From the detail you gave me, this is a in vitro experiment as opposed to like inside a cell where you got both DNA and RNA, basically they made some nucleic acid sequence, add it to a tube containing some other nucleic acid sequence, and observed that the 2 sequences hybridize.
       

      AlphaMagnum

      Full Member
      Jul 14, 2011
      40
      0
      1. Pre-Medical
        Oh, ok that clear up a lot. This is a very simple question and you got it wrong because you were overthinking it.
        All they are asking you is that: why did the two strand of DNA/RNA (doent matter which one it is) bind to each other?
        the right answer is that they are complementary. if they are identical they wouldnt be able to bind.
        From the detail you gave me, this is a in vitro experiment as opposed to like inside a cell where you got both DNA and RNA, basically they made some nucleic acid sequence, add it to a tube containing some other nucleic acid sequence, and observed that the 2 sequences hybridize.

        I guess that makes sense. If you remove RNA from the equation, then the best explanation for two sequences hybridizing is that they are indeed complementary.
         
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