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203 FINAL EXAM PRACTICE QUESTIONS 1. Molecule I below acts as an inhibitor of an enzyme. It is proposed that binding occurs through an electrostatic interaction with an aspartic acid sidechain in the protein. Quaternization of the amino group to form inhibitor II, would fix the positive charge at all pH’s. This, it is suggested, would enhance the electrostatic attraction, and therefore the binding affinity. (13) Binding data for the 2 inhibitors, acquired at 2 temperatures, appears below: x 10 4 M -1 *Be careful of the units when reading values from graphs. Ask yourself whether the values you obtain make sense (a) Calculate: n , the number of binding sites on the enzyme, and K 290K , K 315K , and o 290K ΔG , o 315K ΔG , for the binding of both inhibitors. Does either inhibitor bind in a cooperative or anticooperative manner? (b) Calculate H o and S o for the binding of both inhibitors (c) Is the data consistent with an increase in electrostatic binding on quaternization of the inhibitor as proposed? Explain.
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Chem.203 2. We would like to obtain a measure the stability of a protein at 25 o C in comparison with that of a small DNA at the same temperature.. DSC data acquired for the 2 macromolecules are: For both macromolecules: T m = 73 o C, and H den o at T m = 141.4 kJ mol -1 For the protein C P = 3.6x10 3 J mol -1 K -1 , and C P 2245 0 for the DNA (12) (a) From the data given calculate, for each case, the percentage of the macromolecule in the solution that is in the denatured form at 25 o C . (b) Make a sketch of a van’t Hoff plot ( nK versus 1/T) between 0 and 73 o C for both the DNA and. the protein. The plot need not be quantitative but should display the correct general trend, particularly at T = 0, 34 and 73 o C. 3. Consider the processes (a) (e) listed below under the conditions indicated: (5) (a) H O( ) 2 H + + OH - : [H + ] = [OH - ] = 1.0 M, T = 298K, (b) glucose (0.1 M) glucose (0.01 M), T = 310K (c) ATP hydrolysis, T = 310K, [ATP] = [ADP] = [Pi] = 0.1 mM (d) denDNA(1.0 mM) natDNA (1.0 mM), T = Tm
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