Key HW 2 Fall, 2009

Key HW 2 Fall, 2009 - 1 of 4 Biological Sciences 102 Fall,...

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1 of 4 Biological Sciences 102 Answer Key Fall, 2009 K. Hilt Homework #2 1. Amino acid analysis is done on protein “Z”. The following results are obtained: Amino Acid Number of Residues in Protein “Z” Amino Acid Number of Residues in Protein “Z” A 13 B 13 G 12 W 6 P 5 H 12 Z 24 C 4 K 8 V 24 R 12 S 12 L 23 T 14 Y 12 F 13 a) Calculate the net charge, to the nearest 0.01, of protein “Z” at pH 7. Use the pK a ’s given in homework #1. –16.4 Some things to note: 1) B and Z must be considered as D and E, each with a negative charge at pH 7, since no NH 4 + was reported. (Had there been 13 residues of NH 4 + , we would have known that 13 residues of either B or Z were actually N or Q, with no charge on their side chain). 2) In the intact protein, only the side chains of the “magic 7” and the N- and C-termini contribute a charge. For the side chains, you need to multiply the charge by the number of those residues. b) What is the molecular weight of protein “Z”? Use the value of 110 Daltons as an average molecular weight of an amino acid residue. 22,770 c) At pH 7, would you use a cation exchanger or anion exchange resin to bind protein Z, in order to do ion exchange chromatography? anion exchanger d) Does protein “Z” have quaternary structure? How would you experimentally confirm this? We do not know, from the information given above. What would you propose, to find out? 2. Would Sanger’s N-terminal chemistry work if the DNP-labeled N-terminal residue was extracted using diethylether with 6 N NaOH instead of diethylether with 6 N HCl? Explain. No. (You explain why).
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2 of 4 3. Amino acid analysis of one mole of a peptide yields two moles of methionine, two moles of cysteine, one mole of arginine, and one mole of alanine. Determine the sequence of this peptide from the following information: a) treatment of the intact peptide with phenylisothiocyanate, followed by acid hydrolysis yields PTH-A; b) treatment of the peptide with cyanogen bromide yields a single amino acid (M) and a pentapeptide; c) treatment of the original peptide with trypsin yields a single product; d)
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This note was uploaded on 12/03/2009 for the course ENT 100 taught by Professor Kimsey,r during the Fall '08 term at UC Davis.

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Key HW 2 Fall, 2009 - 1 of 4 Biological Sciences 102 Fall,...

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