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genetics question

Discussion in 'MCAT Discussions' started by pezzang, May 7, 2007.

  1. pezzang

    pezzang Senior Member 10+ Year Member

    May 12, 2005
    Does anybody know how to find GC frequency? I have looked up online but couldn't find it. Do you count GC portion only or G and C separately?
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  3. bluesTank

    bluesTank Zombie 5+ Year Member

    Feb 2, 2007
    College Station, TX
    I've never heard of finding a "GC Frequency"

    Is that some property inherent to a certain species?

    I guess if you had a strand, you would count the G-C pairs, and the frequency would be (G-C pairs) / (total pairs)
  4. mongrel

    mongrel Assoc. Prof. Dogsuit 5+ Year Member

    I think bluesTank is correct with his math. Another way to answer the question is how to find relative GC frequency from a lab experiment. This could be done by measuring the 260 nm absorbance of your dsDNA sample as you increase the temperature. Once you get to the "melting temperature" where your double-strand becomes two single-strands (and absorbance increases), you can compare it to another sample with a known GC freq. Melting temp should increase as GC freq increases due to more hydrogen bonds between the two strands.
  5. DocInProgress

    DocInProgress 7+ Year Member

    Jan 1, 2007
    I think the GC frequency is beyond the scope of the MCATs as I have never encountered that term in the Kaplan and the EK books.
  6. badasshairday

    badasshairday Vascular and Interventional Radiology 10+ Year Member

    Apr 6, 2007
    So A=T is two H-bonds between them. G C pair has 3 H-bonds...
  7. CATallergy

    CATallergy 2+ Year Member

    Jan 23, 2007

    my guess: every bond between the 2 DNA strands is either GC or AT. for example, you might say that some promoter sequence has a high AT frequency. in your example, 11 out of the 16 nucleotides are G or C (and h-bond to C and G, resp. & not shown). 11/16 = about 70%

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