Question

I figured out (a) already so I'm looking for help on (b). Also, in which direction will the positively charged protein feel a force due to the DNA backbone? A vector needs to be drawn.

Question &: The backbone of DNA is highly negatively charged. This net charge arises from the phosphate groups along the backbone of each chain, where each phosphate group has a net charge of -le (a) Consider the phosphate groups to be separated by 3.4 A. What is the force between adjacent groups? Is it attractive or repulsive? (b) Now, imagine a protein is nearby, which has a +le charge that is 5 A away from the DNA backbone, and is situated directly between two phosphate groups as shown. Below is a sketch of the geometry of the problem, labeling the charges and the distances between them. Determine the angle θ.

Answer 1

5A

from the figure we represented 4 points A,B,C,D

$\fn_phv tan\theta$ in a right angled triangle is given by

  $\fn_phv tan\theta$ = side opposite to $\fn_phv \theta$ / side adjacent to $\fn_phv \theta$

=> $\fn_phv tan\theta=\frac{BC}{AB}$

but   $\fn_phv BC=\frac{DC}{2}$

=>   $\fn_phv tan\theta =\frac{DC}{2(AB)}$

=> $\fn_phv tan\theta =\frac{3.4}{2(5)}$

=> $\fn_phv tan\theta =0.34$

=>   $\fn_phv \theta=tan^{-1}(0.34)$

=> $\fn_phv \theta=18.78^{o}$