Chapter 24: Q20P (page 1282)
Show the third and fourth steps in the sequencing of oxytocin. Use figure 24-14 as a guide.
Short Answer


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Chapter 24: Q20P (page 1282)
Show the third and fourth steps in the sequencing of oxytocin. Use figure 24-14 as a guide.


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Draw the resonance forms of a protonated guanidino group and explain why arginine has such a strongly basic isoelectric point.
Complete hydrolysis of an unknown basic decapeptide gives Gly, Ala, Leu, Ile, Phe, Tyr, Glu, Arg, Lys, and Ser. Terminal residue analysis shows that the N terminus is Ala, and the C terminus is Ile. Incubation of the decapeptide with chymotrypsin gives two tripeptides, A and B, and a tetrapeptide, C. Amino acid analysis shows that peptide A contains Gly, Glu, Tyr, and; peptide B contains Ala, Phe, and Lys; and peptide C contains Leu, Ile, Ser, and Arg.Terminal residue analysis gives the following results.

Incubation of the decapeptide with trypsin gives a dipeptide D, a pentapeptide E, and a tripeptide F. Terminal residue analysis of F shows that the N terminus is Ser and the C terminus is Ile. Propose a structure for the decapeptide and for fragments A through F.
Write the complete structures for the following peptides. Tell whether each peptide is acidic, basic, or neutral.
There are many methods for activating a carboxylic acid in preparation for coupling with an amine. The following method converts the acid to an N-hydroxysuccinimide (NHS) ester.

(a) Explain why an NHS ester is much more reactive than a simple alkyl ester.
(b) Propose a mechanism for the reaction shown.
(c) Propose a mechanism for the reaction of the NHS ester with an amine, R-NH2
Show how you would use the Strecker synthesis to make isoleucine. What stereochemistry would you expect in your synthetic product?
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