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문제 1a
Explain why, when the imidazole ring of histidine is protonated, the double-bonded nitrogen is the nitrogen that accepts the proton.
문제 1b
Explain why, when the guanidino group of arginine is protonated, the double-bonded nitrogen is the nitrogen that accepts the proton.
문제 5
Alanine has pKa values of 2.34 and 9.69. Therefore, alanine exists predominately as a zwitterion in an aqueous solution with pH >____ and pH <____.
문제 8a
Draw the predominant form for glutamate in a solution with the following pH:
a. 0
문제 8b
Draw the predominant form for glutamate in a solution with the following
pH: b. 3
문제 9b
Why is the pKa of the arginine side chain greater than the pKa of the lysine side chain?
문제 11a,b
a. Which amino acid has the lowest pI value?
b. Which amino acid has the highest pI value?
문제 11c
c. Which amino acid has the greatest amount of negative charge at pH = 6.20?
문제 11d
d. Which amino acid has a greater negative charge at pH = 6.20, glycine or methionine?
문제 13
a. What percentage of the a-amino group of lysine will be protonated at its pI?
<25%, 50%, >75%
b. Answer the same question for the e-amino group of lysine
문제 14
Explain why the pI of lysine is the average of the pKa values of its two protonated amino groups.
문제 16
A mixture of seven amino acids (glycine, glutamate, leucine, lysine, alanine, isoleucine, and aspartate) is separated by chromatography. Explain why only six spots show up when the chromatographic plate is coated with ninhydrin and heated.
문제 18a
Explain the order of elution (with a buffer of pH 4) of the following pairs of amino acids through a column packed with Dowex 50:
a. aspartate before serine
문제 18b
Explain the order of elution (with a buffer of pH 4) of the following pairs of amino acids through a column packed with Dowex 50:
b. serine before alanine
문제 20
Why is excess ammonia used in the preceding reaction?
문제 22a
What amino acid is formed using the N-phthalimidomalonic ester synthesis when the following alkyl halides are used in the third step?
a.
문제 22b
What amino acid is formed using the N-phthalimidomalonic ester synthesis when the following alkyl halides are used in the third step?
b. CH3SCH2CH2Br
문제 23a
What alkyl halide is used in the acetamidomalonic ester synthesis to prepare
a. lysine?
문제 23b
What alkyl halide is used in the acetamidomalonic ester synthesis to prepare
b. phenylalanine?
문제 24b
What amino acid is formed when the aldehyde used in the Strecker synthesis is
b. 2-methylbutanal?
문제 25
Esterase is an enzyme that catalyzes the hydrolysis of esters. It hydrolyzes esters of l-amino acids more rapidly than esters of D-amino acids. How can this enzyme be used to separate a racemic mixture of amino acids?
문제 26
Draw the tetrapeptide Ala-Thr-Asp-Asn and indicate the peptide bonds.
문제 27
Draw the resonance contributors of the peptide bond in the less stable configuration.
문제 28
Which bonds in the backbone of a peptide can rotate freely?
문제 29
An opioid pentapeptide has the following structure: Tyr-Cys-Gly-Phe-Cys
a. Draw the structure of the pentapeptide including all the side chains.
b. Write its structure following mild oxidation.
문제 30
What is the configuration about each of the asymmetric centers in aspartame?
문제 32
What dipeptides would be formed by heating a mixture of valine and N-protected leucine?
문제 34
Show the steps in the synthesis of the tetrapeptide Leu-Phe-Ala-Val.
문제 35
a. Calculate the overall yield of bradykinin when the yield for the addition of each amino acid to the chain is 70%.
b. What would be the overall yield of a peptide containing 15 amino acids if the yield for the incorporation of each is 80%
문제 36
Show the steps in the synthesis of the tetrapeptide in Problem 34, using Merrifield's method.
