Chapter 2, Problem 2.42NP

DNA can be modeled as an elastic rod that can be twisted or bent. Suppose a DNA molecule of length L is bent such that it lies on the arc of a circle of radius ${\text{R}}_{\text{c}}$. The reversible work involved in bending DNA without twisting is $wbend=\frac{BL}{2R_c^2}$ where B is the bending force constant. The DNA in a nucleosome particle is about 680. A in length. Nucleosomal DNA is bent around a protein complex called the histone octamer into a circle of radius $55\stackrel{0}{A}$. Calculate the reversible work involved in bending the DNA around the histone octamer if the force constant $B=2.00\times {10}^{-28}\text{J}\text{m}$.