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miniexam - BCH 4053 August 3, 2001 Mini-Exam NAME_ Answer...

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BCH 4053 August 3, 2001 Mini-Exam NAME_____________________ Answer question 1 or 2 (20 points) 1. (a) How many mL of 0.1 M NaOH must be added to 100 mL of 0.05 M formic acid to make a buffer solution with a pH of 4.25? (b) How many mL of 0.1 M sodium formate must be added to 100 mL of 0.05 M formic acid to make a buffer solution with a pH of 4.25? (Formic acid has a pK of 3.75.) 2. Draw the structure of the following peptide, showing all dissociable functional groups in their fully protonated form, and indicate the approximate pK of each of the dissociable functional groups: Page Points 1 ____ 2 ____ 3 ____ 4 ____ 5 ____ Total ______ Lys.Cys.Arg.Tyr.Glu (a) What is the charge on the fully protonated form of the peptide? (b) What is the charge on the fully unprotonated form of the peptide? (c) What is the approximate pI of the peptide? (d) What is the net charge on the peptide at pH 6.0?
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BCH 4053 –Mini-Exam Page 2 Name________________________ Answer question 3 or 4 (15 points) 3. You have isolated an octapeptide with the amino acid composition (Lys 2 , Asp, Tyr, Phe, Gly, Ser, Ala) Reaction of the intact peptide with FDNB yields DNP-alanine. Cleavage with trypsin yields peptides with compositions (Lys, Ala, Ser) and (Gly, Phe, Lys) plus a dipeptide. Reaction with chymotrypsin releases free aspartic acid, a tetrapeptide with composition (Lys, Ser, Phe, Ala) and a tripeptide with composition (Gly, Lys, Tyr). What is the sequence? (Explain your reasoning). 4.
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miniexam - BCH 4053 August 3, 2001 Mini-Exam NAME_ Answer...

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