CumFinal-2009 - CUMULATIVE FINAL EXAM: VERSION 1 (MARK 1 IN...

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CUMULATIVE FINAL EXAM: VERSION 1 (MARK 1 IN FIRST COLUMN OF “DAY” ANSWER ALL QUESTIONS ON THE OPSCAN SHEET WITH PENCIL 8 1. You are separating amino acids and peptides on a gel filtration column of crosslinked dextran beads (Sephadex™) beads. Which one of these emerges from the column last? a. isoleucine b. glutamyl-glutamic acid (glu-glu) c. (his) 6 [this hexapeptide is known as a “his-tag”] d. lysine e. alanine 2. Which statement best describes a strategy you could use to overcome the contribution of the “hydrophobic effect” to the structure of a peptide dissolved in an aqueous medium? a. you could increase the ionic strength of the solvent and enhance the solvation of nonpolar side chains like leucine by water. b. you could add a second polypeptide like polyleucine to the aqueous solvent which would bind up all of the clatherates in the water. c. you could use a detergent to disrupt the hydrogen bonds in the interior of the peptide that normally keep the nonpolar side chains buried. d. you could use a chaotropic agent to diminish the unfavorable entropy imposed by nonpolar side chains on the aqueous solvent as a result of formation of clatherates. e. you could titrate the polar side chains to reach the isoionic point of the peptide, at which point the contributions of entropy and enthalpy would cancel each other out. 3. The pI (isoionic point) of the hexapeptide NH 2 -ala-ser-his-lys-glu-thr-COOH lies: a. between pH 2 and pH 5 b. at pH 5 c. between pH 2 and pH 10 d. between pH 6.5 and pH 9 e. between pH 9 and pH 10 4. You are sequencing a nonapeptide (nine amino acids). Which statement is most consistent with the results you would obtain. a. if you first treated the peptide with staphylococcal V8 protease and then reacted the mixture of products with dansyl chloride, and if you then were able to isolate two dansylated peptides from the mixture, you would conclude that the C-terminus of at least one of the two dansylated peptides was methionine. b. if you first treated the peptide with chymotrypsin and then reacted the mixture of products with dansyl chloride, and if you then were able to isolate a dansylated tetrapeptide and a dansylated pentapeptide from the mixture, you would expect to find that the amino- terminus of at least one of the two dansylated peptides was tyrosine or phenylalanine. c. if you treated the peptide with phenyl isothiocyanate in a nonaqueous acid like trifluoroacetic acid and then treated the mixture of products with an aqueous acid, it is possible that you might find one octapeptide and a derivative of a single amino acid after sequential exposure to the two solvents. d. if you treated the peptide with cyanogen bromide and failed to observe any cleavage, you would suspect that the peptide has its amino-terminus blocked. e. if there are no products shorter than nine amino acids after exhaustive digestion of the
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CumFinal-2009 - CUMULATIVE FINAL EXAM: VERSION 1 (MARK 1 IN...

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