W_07_215_E3_key - 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. 5.66 2.20 9.59 g) Draw the structure/s of tyrosine in solution at pH 10.07. 6 2 22 CH 3 H Ala NH 2 CO O Pro O O CH 2 Glu Asp Lys O O CH 2 CH 2 (Note: if necessary to demonstrate the nature of R, you may draw the entire amino acid at pH 7 ) H H 3 NC C CH 2 O O OH H H 2 C CH 2 O O OH H H 2 C CH 2 O O O H 2.20 5.66 9.11 9.59 10.07 R group 3-letter abbreviation Gly Gly may or may not be circled (CH 2 ) 4 NH 3 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
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W_07_215_E3_key - Name:_ Page 1(W.07.215.E3 p1) I (24...

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