TPR Test #2 Question 24

Discussion in 'DAT Discussions' started by carl_maslow, Sep 7, 2014.

  1. carl_maslow

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    Hi guys,

    I need your help with a question from TPR (Crack the DAT) online Test 2 # 24:

    A messenger RNA (mRNA) has the sequence UUACCGCUAA, which of the following was the DNA sequence from which the mRNA was transcribed?

    A) UUAGCGGUAA
    B) TTAGCGGTAA
    C) AAUGGCGAUU
    D) TTAGGCGATT
    E) AATGGCGATT



    On page 119 of their book, they wrote the following:

    The end of the chain with a free 5’ phosphate group is written first in a polynucleotide, with other nucleotides in the chain indicated in the 5’ to 3’ direction.

    Given their textbook information, I assumed UUACCGCUAA is 5- UUACCGCUAA – 3. Since the template strand is used to transcribe mRNA (which is read 3 – 5 since mRNA is made in 5-3 direction), I thought the DNA sequence should be 3 – AATGGCGATT -5. If I write the free 5’ phosphate group first, the answer should be 5- TTAGCGGTAA – 3. So the answer is B.

    To put it simply:

    Template strand: 3 – AATGGCGATT -5
    mRNA: 5- UUACCGCUAA – 3

    Answer written in format outlined by the textbook: 5- TTAGCGGTAA – 3
    Therefore, the answer is B.




    But the answer B is wrong. They claim the answer is E, and so does similar question in CliffNotes AP Biology Test 2 Question 14.

    Given the TPR #2 test and Cliff Test 2, I’m assuming they don’t expect you to twist things like what I did – and keeps thing simple. But I just don’t get what I am doing wrong or why B shouldn’t be the right answer. I keep telling myself that they just don’t expect you to think so complicated, but I am hoping to get a better explanation to prove my thought process (thus answer B) wrong. Could you guys give any feedback on this type of question please?

    I would really appreciate your help.

    Thank you in advance.
     
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  3. shyfox9p

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    They didn't give you the directionality, so you can't assume there is one. It seems like you know the material, but thought too much on the question. Keep at it.
     

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