NS FL # 2 B/B Passage 10

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  1. orangeblue

    7+ Year Member

    Feb 10, 2011
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    #51. If the neomycin resistance gene on the pC27-53 and pC27-53X plasmids was located closer to the gene encoding for p53, which of the following results would most likely be observed?

    There would be a decrease in the number of colonies in all trials.

    The number of colonies observed for CRC157 and CRC184 transfected with pC27-53 would decrease. (CORRECT ANSWER)

    The number of colonies observed for CRC169 transfected with pC27-53 and pC27-53X would decrease.

    The number of colonies observed for CRC169 transfected with pC27-53 and pC27-53X would increase.

    Basically, they are saying that if the neomycin resistance gene is too far (as it is currently in the passage diagram), sometimes the cells wouldn't translate/transcribe it and the cell will not have the resistance. So it will die and not show up in the # of cell count. This is one of the reasons why the pC27-53 cell # chart is low, not only b.c p53 supresses uncontrollable cell growth in cancer cells.

    when you put the genes close to each other, you will get the effects of p53 (which is control too much cell division/growth) with gene resistance so cells wouldn't die b.c neomycine resistance gene is being transcribed/translated.
    kinda confused here...

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    #1 orangeblue, Aug 14, 2015
    Last edited: Aug 14, 2015
  2. ElectricNoogie

    ElectricNoogie MCAT enthusiast

    Apr 30, 2015
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    Fellow [Any Field]
    This question requires a good understanding of the experimental setup and the concept of genetic linkage. Generally speaking, the closer 2 genes are to eachother on a chromosome, the MORE likely they are to be inherited together during cell division.

    If the NeoR gene AND the p53 gene were closer, that would increase the odds of a given cell produced to have BOTH genes. Thus, any cell line that got these 2 genes successfully could be slowed in their reproduction (thanks to the working p53) and any cells that did survive would survive the gentamycin treatment.

    Choices C and D refer to line 169, which, like BT134, showed no effect when treated with WT p53, compared to the mutant p53. This suggest that either the WT p53 was not taken up by the cells or that in the mutant p53 case, there was a working p53 gene already which kep the cell count low. We know they both got the NeoR gene because they survived the gentamycin treatment. Some cells managed to get the NeoR gene and survived the gentamycin treatment. Thus, it not as likely these cells would change much due to the new proximity as it appears the WT and defunct p53 gene transfection had the same results suggesting whether you provide an additional working p53 or not, the cell count stayed low and non-cancerous.

    Hope this helps, Good luck!

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