I am not sure how to do this physics problem

Question

What is the potential energy (the binding energy) between a  pair and a nearby  pair arranged as seen below. These pairs are part of guanine and cytosine respectively in a DNA molecule. The molecules are covalently bonded and so the atoms share electrons. The  pair each has a charge of . The  pair each has a charge of . 

 

Note we're not asking about the binding of the  to the  . We're only asking about the binding between the  pair to the  pair. 

The spacings are given in nm = nanometers. 1 nm =  m.  

Hint: The total PE between the pairs is comprised of 4 terms: 

 

Answer 1

Hi Dylan A.,

Your image didn't open, but I get the picture anyway. So assume that the stated charge imbalances are really those amounts of charge at each of the nuclei stated. If you're given all the relevant distances, so be it -- if you need to calculate any of them you probably can from the data set given using geometry. Then, you do the PE calculations: PE = -kq1q2/r , if I'm not mistaken. You can find the k constant in your electrostatics laws. Total up the PEs, bearing in mind that ++ pairings have a +PE, and +- pairings have a -PE signage! You should get a net -PE (PE<0) value, since the CG nucleoside pair does stick together.

-- Cheers, -- Mr. d.