Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Biology and the DNA/nucleotides Please help due tomorrow

  1. May 20, 2010 #1
    1. The problem statement, all variables and given/known data

    Erwin Chargaff discovered that although the nucleotide composition of DNA varies from one species to another,that composition always follows certain rules. While the variation in nucleotides helps to explain the complexity of life, the physical structure of the DNA itself can also help certain organisms adapt to particular environments. Imagine you are working with a research team sampling the ocean floor near a hot vent that releases a steady stream of
    hot water. The hot water has a temperature of about 45°C, while the surrounding ocean has a temperature of 6°C.

    Your team collects two samples of bacteria — one from the mouth of the hot vent, and one from the ocean floor about 20 m away. When you return to the lab, you isolate the DNA from these bacteria to determine their nucleotide composition. The table shows the results of your test for the adenine content of the DNA.

    Apply what you have learned about Chargaff’s findings and
    DNA composition to solve the following problems.

    1. Complete the table to determine the amounts of the
    other nucleotides found in each DNA sample.

    2. For each DNA sample, draw a linear stretch of DNA
    about 15 nucleotides long, with a nucleotide
    composition that corresponds to its data set. With a
    dotted line, illustrate the hydrogen bonds between
    complementary base pairs.

    3. Considering the bonds between base pairs, which
    of these DNA samples is most likely taken from the
    bacteria collected at the mouth of the hot vent?
    Explain your answer.

    I filled out the stuff in the red

    2. The attempt at a solution

    I have a hard time doing the second question, which is to draw the thing, can you please help me, i try to then i get decimal stuff to draw such as since adenine is 31%, thus (.31)(30) = 9.3

    how can i draw .3 of adenine. or am i doing something wrong, please help me with the second and the third question.

    i got this assignment due tomorrow Please help, i would really appreciate it.



    Please help, its due tomorrow. Thank you so much.
  2. jcsd
  3. May 25, 2010 #2
    You have everything you need, including a template for the drawing. For 2, Just approximate the ratio, you cannot draw .3 of any molecule. So you have 62% A/T to 38% G/C. You need a strand that is about 15 base pairs in length. So multiply 15 by 0.62 = 9.3 A/T pairs ≈ 9 pairs. The same for G/C, 15 by 0.38 = 5.7 G/C pairs ≈ 6 pairs. For 3, think about the hydrogen bond in water for example. What makes such a small molecule have such a high boiling point? The bond dissociation energy of hydrogen bonds. Now if you were a bacteria living in the hot vent, which composition would you want to survive? A base pair composition with more or less hydrogen bonds? Ask yourself the same question for the bacteria living away from the hot vent.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook