1. The peptide Special K forms an a-helix that is broken at high temperatures. The fraction of peptide in the a-helical form, oh, was measured over a range of temperatures: T(K) 324.4 326.1 327.5 329.0 330.7 332.0 333.8 0.961 0.893 0.787 0.595 0.345 0.167 0.045 a. Calculate the equilibrium constant, Keq, and molar free energy for helix formation, AG, at 324.4 K. b. What is the sign of AH (i.e., positive or negative) for the formation of an a-helix at this temperature? Provide a brief explanation for its sign. c. Special K contains one histidine residue. Calculate the fraction of Special K molecules in which the histidine is positively charged at 25C and pH 7.0. d. As the temperature of the peptide is increased, the Ka of the histidine residue will change. Note from Table 4.2 that the AH for the dissociation of a histidine side chain (i.e., transition of charged to uncharged) is +29.9 kJ/mol. Based on this, will the fraction of charged histidine residues increase or decrease as the temperature is raised from 25C to 54.4C at pH 7? You don't need to calculate a value, but explain your reasoning