Organic Chemistry 354 Quiz - December 3, 1999

Dr. Sundin

1. Determine the amino acid sequence of a decapeptide based on the following analytical data. Edman degradation gave Val. Carboxypeptidase A hydrolysis gave Ala.

Total hydrolysis:

    Ala = 3

    Phe = 1

    Ser = 2

    Tyr = 1

    Val = 3

Partial hydrolysis gave a complex mixture from which only five tripeptides (see below) were isolated in high enough yield and purity to be characterized. They are:

    Ala-Ala-Phe

    Phe-Val-Val

    Tyr-Ser-Ala

    Val-Tyr-Ser

    Val-Val-Ser

Answer

2. In solution at a pH of 3.22, Glutamic Acid (Glu) has a net charge of zero.

a. Give the detailed structure of the predominant species at pH = 1. Answer

b. Give the detailed structure of the predominant species at pH = 11. Answer

c. Peptides also exhibit different net charges at different pH’s. Glu-Glu-Glu, determine the net charge at pH’s of 1 and 11. Answer

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