Two polynucleotides with sequences AnUn (where A and U denote adenine and uracil, respectively) interact through A-U base pairs, forming a double helix. When n = 5 and n = 6, the equilibrium constants for formation of the double helix are 5.0 × 10^3 and 2.0 × 10^5, respectively. (a) Suggest an explanation for the increase in the value of the equilibrium constant with n. (b) Calculate the contribution of a single A-U base pair to the Gibbs energy of formation of a double helix between AnUn polynucleotides.