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Exam 24: Amino Acids, Peptides, and Proteins

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Question 21

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Which of the following compounds would reduce a disulfide linkage in a peptide?

A) urea
B) concentrated NaOH
C) dithiothreitol
D) dilute HCl
E) bromine

F) A) and E)
G) B) and E)

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Question 22

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Bradykinin is a nonapeptide released by globulins in the blood in response to a wasp sting. Hydrolysis gives the following amino acids: 2 Arg, Gly, 2 Phe, 3 Pro, and Ser. Edman degradation gives phenylthiohydantoin of Arg. Cleavage with carboxypeptidase gives Arg. Partial hydrolysis gives the following di- and tripeptides: Phe-Ser, Pro-Gly-Phe, Pro-Pro, Ser-Pro-Phe, Phe-Arg, and Arg-Pro. What is the amino acid sequence of bradykinin?

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Arg-Pro-Pr...

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Question 23

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Which method gives you information about the N-terminus end of a peptide?

Provide a detailed, stepwise mechanism for the Strecker synthesis of racemic alanine from acetaldehyde.

What is the major force responsible for the formation of an α-helix in protein secondary structure?

Which of the following amino acids are classified as essential amino acids? (More than one answer is possible.)

Provide a structure of the dipeptide Ala-Ser.

Provide a reasonable synthesis of racemic alanine from ethanol.

Given the following pKa values, what is the major ionization state of histidine at pH 11? (α-COOH = 2.0, α-NH₃⁺ = 9.0 and R-group imine = 6.5)

Treatment of a peptide which contains disulfide linkages with peroxyformic acid yields a peptide which contains what new amino acid residue?

Amino acids have ________.

Which of the following fragments would not result when the decapeptide Asn-Gly-Lys-Phe-Pro-Arg-Gly-Leu-Lys-Ser is treated with trypsin?

Provide the structure of the predominant form of alanine present in an aqueous solution at a pH of 2.0.

A student proposed to make aspartic acid from succinic acid using Br₂/PBr₃, then adding a large excess of NH₃. Why might this synthesis not work?

How many standard amino acids are there?

Which of the following arrangements is usually not found in the secondary structure of proteins?

Give a detailed, stepwise mechanism for the formation of the activated acyl derivative from the reaction of an amino acid with N,N'-dicyclohexylcarbodiimide.

Which of the following amino acids does not have an aromatic substructure within its side chain?

Provide the structure of the predominant form of L-methionine present in an aqueous solution at biological pH, pH = 7.4.

How would you make tryptophan using the Strecker Synthesis?