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pset I-2011-a - compared to 1M 4(24 pts The protein...

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1Problem Set I Bioc 545/645 Due no later than 5 PM, Thursday, September 1, 2011 1. (10 pts) Calculate the pH when 10 ml 1.0 M HCl is added to: a) 990 ml of pure water [Hint: HCl is totally dissociated so [HCl]=[H + ]] b) 990 ml of 0.1 M sodium phosphate buffer, pH 7.0 (pK 1 = 2.15, pK 2 = 6.8, pK 3 = 12.4) [Hint: first calculate the ratio of weak acid to conjugate at pH 7.0 for the phosphate buffer and then recalculate pH assuming the HCl converts and equal amount of conjugate base to weak acid.] 2. (10 pts) How many grams of solid tris-(hydroxymethyl)-aminomethane (Tris base, MW = 121 g/mol) and how many ml of 1 M HCl must be mixed to produce 500 ml of 0.05 M Tris buffer, pH 7.6? (pKa = 8.4 at 25 °C). 3. (10 pts) Calculate the pH of a 1 M solution of acetic acid (pK = 4.76). You may assume that the [H + ] can be ignored compared with the 1 M starting concentration of acetic acid. [You can’t use the Henderson Hasselbach on this one. Let x = [acetate] which will also equal [H+], and then HA = [1M –x]. You can assume that 1M-x = 1M since x should be small
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Unformatted text preview: compared to 1M.] 4. (24 pts) The protein chymotrypsinogen can exist in two states: a native state (N) characterized as a compact, organized globule, and a denatured state (D) characterized by disorder and randomness. The relative amount of the two states depends on solution conditions such as temperature and pH as described by the following equilibrium: N ↔ D K eq = [D]/[N]. ΔG o = +3.56 kJ/mol based on the equilibrium constant at 327 K. a) Calculate K eq at this temperature (Use R = 0.008314 kJ/mol/ o K). b) From the temperature dependence of K eq , it was determined that ΔH o at 327 K is +0.533 kJ/mol. Calculate ΔS o at this temperature. c) Is the denaturation reaction favorable or unfavorable in terms of the change in enthalpy? Is the denaturation reaction favorable or unfavorable in terms of the change in entropy? d) Is the protein denatured at 327 K?...
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