Chapter 21: 21-47P (page 1024)
Which would have the greatest percentage of polar amino acids, a spherical protein, a cigar-shaped protein, or a subunit of a hexamer? b. Which would have the smallest percentage of polar amino acids?
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Glutathione is a tripeptide whose function is to destroy harmful oxidizing agents in the body. Oxidizing agents are bought to be responsible for some of the effects of aging and to play a causative role in cancer.
Glutathione removes oxidizing agents by reducing them. In the process, glutathione is oxidized, resulting in the formation of a disulphide bond between two glutathione molecules. An enzyme subsequently reduces the disulphide bond, returning glutathione to its original condition so it can react with another oxidizing agent.
a. What amino acids make up glutathione?
b. What is unusual about glutathione’s structure?
What aldehydes are formed when the following amino acids are treated with ninhydrin?
a. tyrosine b. leucine c. arginine
Explain the difference in the \({\bf{p}}{{\bf{K}}_{\bf{a}}}\) values of the carboxyl groups of alanine, serine, and cysteine.
Show the peptides that would result from cleavage by the indicated reagent:
a. Val-Arg-Gly-Met-Arg-Ala-Ser by carboxypeptidase A
b. Ser-Phe-Lys-Met-Pro-Ser-Ala-Asp by cyanogen bromide
c. Arg-Ser-Pro-Lys-Lys-Ser-Glu-Gly by trypsin
Explain why the pI values of tyrosine and cysteine cannot be determined by the method described on page 995.
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