Problem Set #1

Problem Set #1 - Biology 100 Fall 2009 Problem Set#1 due...

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Biology 100 Fall, 2009 Problem Set #1 due: October 5 (1). (a) For each of the following amino acids: L-lysine L-glutamic acid L-histidine L-valine draw structures for predominant ionic forms at (i) pH 2.0, (ii) pH 7.0, and (iii) pH 12.0. (b) For L-histidine, also draw the second-most abundant ionic form at pH 7.0. (c) What would be the molar ratio of these two, ionic forms of L-histidine at pH 7.0? (2). A 1 M aqueous solution of an unknown L-amino acid has two dissociable groups with pK a (1) = 2.0 and pK a (2) = 11.0. (a) Assuming you have started with one liter of the pure, acidic form of the compound, and assuming the NaOH titrant does not measurably change the solution volume, calculate and fill-in the following table: NaOH titrant added (moles) measured pH 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 (b) On a sheet of graph paper, draw the titration curve of this amino acid solution. On your graph denote: pK a (1), pK a (2), and pI (the isoelectric point). (c) Write the acid-base reactions occurring at pK a (1) and pK a (2). (d) Which L-amino acid do you suppose constitutes your unknown solution?
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(3). In the laboratory, you are handed a tube containing a highly purified protein in aqueous
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Problem Set #1 - Biology 100 Fall 2009 Problem Set#1 due...

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