Organic Chemistry

Problems 997

53. acids can be prepared by treating an aldehyde with ammonia and hydrogen cyanide, followed by acid-catalyzed
    hydrolysis.
    a. Give the structures of the two intermediates formed in this reaction.
    b. What amino acid is formed when the aldehyde that is used is 3-methylbutanal?
    c. What aldehyde would be needed to prepare valine?


54. The UV spectra of tryptophan, tyrosine, and phenylalanine are shown here. Each spectrum is that of a solution of the
    amino acid, buffered at Calculate the approximate molar absorptivity of each of the three amino acids at 280 nm.


55. A normal polypeptide and a mutant of the polypeptide were hydrolyzed by an endopeptidase under the same conditions. The
    normal and mutant differ by one amino acid residue. The fingerprints of the peptides obtained from the normal and mutant
    polypeptides are as shown. What kind of amino acid substitution occurred as a result of the mutation (That is, the substituted amino
    acid more or less polar than the original amino acid? Is its pI lower or higher?)

Electrophoresis at pH 6.5

Paper chromatography

Electrophoresis at pH 6.5

Paper chromatography

Normal Mutant

−

+

−

+

0

Absorbance

.6

.5

.4

.3

.2

.1

230 240 280 290 300

Wavelength (nm)

260 270 310

tryptophan

tyrosine

phenylalanine

250

pH=6.0.

1 * 10 -^3 M

a-Amino

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