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exam1_chem430_spring2008-1-1

exam1_chem430_spring2008-1-1 - Hogan_chem430_s2008 1 Exam1...

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Hogan_chem430_s2008 Exam1 1. Determine the ratio of the PROTONATED to DEPROTONATED species of Asp’s R-group at pH 5.5 given the pK R of Asp = 3.86 2. A new amino acid similar to K has been discovered that possesses a side chain with two ionizable functions. The pK R values for these functions are pK R 1 = 9.78 and pK R 2 = 11.42. Assume pK 1 and pK 2 are identical to K. (a) Sketch a titration curve for this new amino acid and label appropriately. (b) Calculate the pI of this amino acid. (c) How many molar equivalents of OH- must be added to this amino acid for it to posses a net -1 charge? 3. Calculate the approximate pI of the polypeptide N’-ATLDAK-C’ (assume pK 1 = 2; pK 2 = 9) 4. The subunits of some multimeric proteins actually associate and form quaternary structure more readily as temperature increases. Show one of the equations from our “life obeys the laws of thermodynamics” discussion and explain in one sentence why higher temperature would make the association of the subunits more favorable. Assume H remains approximately the same before and after subunit association. 5. Using one letter codes, list ALL amino acids whose R-groups can form a salt bridge with the side chain of E at (a) pH 3 (b) pH 7 (c) pH 13 6. Imagine you are overworked and underpaid. You are given a solution containing two proteins (A and B) and two columns (Column 1 and Column 2). The pI values for the two proteins are 4.3 and 9.2, but you don’t know which pI belongs to which protein. You do not know much about
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