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test1 - BCH 4053(10 1 HOUR TEST 1 NAME Vitamin C(ascorbic...

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January 31, 2001 HOUR TEST 1 NAME_____________________ (10) 1. Vitamin C (ascorbic acid) is a diprotic acid, with dissociation constants: pK 1 = 4.1; pK 2 = 11.8. If vitamin C were excreted in the urine of a patient, and the urine had a pH of 4.5, what fraction of the vitamin would carry a negative charge? (Note: I am asking for a fraction and not a ratio ). Page Points 1 ____ 2 ____ 3 ____ 4 ____ Total ______ (14) 2. Draw a titration curve for cysteine on the graph below. (a) Locate and identify the points on the curve corresponding to pK 1 , pK 2 , and pK 3 . (b) Calculate the approximate pI value and locate its position on the curve. (c) Indicate the pH region of the graph in which the side chain functional group is more than 75% charged. (9) 3. Underline the following peptides which are negatively charged at pH 7.0. Circle each amino acid which is aromatic . Put an X through each amino acid that contains a sulfur atom . gln.phe.tyr.ala
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test1 - BCH 4053(10 1 HOUR TEST 1 NAME Vitamin C(ascorbic...

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