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24 Organic and Biological Chemistry Solutions to Exercises = Kw/Kb = 1.0 10⁻¹⁴ 8 10⁻⁵ = 5.55 10⁻¹⁰ = 5.6 10⁻¹⁰ In general, a -COOH group is stronger acid than a group. The lower value for amino acids is for the ionization (deprotonation) of the -COOH group and the higher is for the deprotonation of the group. = 9.47 (c) C C C = 4.07 H By analogy to serine, the carboxyl group near the amine will have ~2 and the amino group will have pKa ~9. By elimination, the carboxyl group in the side chain has ~4. 24.101 (a) Because the native form is most stable, it has a lower, more negative free energy than the denatured form. Another way to say this is that G for the process of denaturing the protein is positive. (b) is negative in going from the denatured form to the folded (native) form; the native protein is more ordered. (c) The four S-S linkages are strong covalent links holding the chain in place in the folded structure. A folded structure without these links would be less stable (higher G) and have more motional freedom (more positive entropy). (d) After reduction, the eight S-H groups will form hydrogen-bond-like interations with acceptors along the protein backbone, but these will be weaker and less specifically located than the S-S covalent bonds of the native protein. Overall, the tertiary structure of the reduced protein will be looser and less compact due to the loss of the S-S linkages; the entropy will be higher. (e) The amino acid cysteine must be present in order for -SH bonds to be found in ribonuclease A. (Methionine contains S, but no -SH functional group.) 24.102 = = 6.2 747