Winter 2007 blank - Name:_ Page 1(W.07.215.E3 p1) I (24...

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Name:_____________________ Page 1(W.07.215.E3 p1) a) (C&E News Apr 17, 2006, 41) Gelatin is a mixture of amphipathic peptides that serves as whipping agents and foam stabilizers in marshmallows such as Peeps. The gelatin polypeptides contain primarily the amino acids: alanine, aspartic acid, glycine, glutamic acid, lysine, and proline. H 3 NH C R 1 O NH H C R 2 O NH H C R 6 O O ...... - generic hexapeptide structure Arrange the six amino acids into a hexapeptide which is amphipathic in nature: 1) in the large box, draw the structure of the R group or the amino acid at pH 7 ; 2) in the small box, write in the three letter abbreviation for the amino acid; 3) circle the R groups that would be hydrophobic. R 1 R 2 R 3 R 4 R 5 R 6 8 b) The amino acid tyrosine is titrated with NaOH. Draw the resulting titration curve on the graph below. equivalents NaOH 0.5 1.0 1.5 2.0 2.5 3.0 pH 0 2 4 8 6 10 14 12 c) What is the pH when 1/2 equivalent of NaOH has been added? d) What is the pH when 2 equivalents of NaOH have been added? I ( 24 points) e) What is the isoeletric point (pI) of tyrosine? f) Draw the structure/s of tyrosine in solution at pH 5.66. g) Draw the structure/s of tyrosine in solution at pH 10.07. 6 2 22 (Note: if necessary to demonstrate the nature of R, you may draw the entire amino acid at pH 7 ) R group 3-letter abbreviation 2 2
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Name:_____________________ Page 2(W.07.215.E3 p2) a) Allose is the C3 epimer of glucose. Draw the Haworth projection of D -(L)-allofuranose H CH 2 OH Br H HO H HB r CH 2 OH C O OCH 3 b) Assign the stereocenters in the following molecule as R or S.
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Winter 2007 blank - Name:_ Page 1(W.07.215.E3 p1) I (24...

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