# Physics

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The two strands of the helix-shaped DNA molecule are held together by electrostatic forces as shown in the Figure 16-44 in the textbook. Assume that the net average charge (due to electron sharing) indicated on H and N atoms is 0.2e and on the indicated C and O atoms is 0.4e. Assume also that atoms on each molecule are separated by 1.0*10^ - 10m.

a)

Estimate the net force between a thymine and an adenine. For each bond (red dots) consider only the three atoms in a line (two atoms on one molecule, one atom on the other). I got 4.6*10-10 N

b)Estimate the net force between a cytosine and a guanine.

7.1*10^-10 N

c)Estimate the total force for a DNA molecule containing 10^5 pairs of such molecules.

• Physics -

I just had to look up the answer, as I couldn't figure it out either. Turns out it is rather simple. You need to add the two together and multiply by n=10^5, but only half of the bonds come from each type of base pair so you need to divide the final result by two to get the right answer. It asks for one sig fig, so it is 6X10^-5.

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