Organic Chemistry

Problems 995

Key Terms

amino acid (p. 959)

D-amino acid (p. 964)

L-amino acid (p. 964)

amino acid analyzer (p. 970)

amino acid residue (p. 959)

anion-exchange resin (p. 970)

antiparallel sheet (p. 990)

automated solid-phase peptide synthesis

(p. 980)

cation-exchange resin (p. 970)

coil conformation (p. 991)

C-terminal amino acid (p. 973)

denaturation (p. 994)

dipeptide (p. 959)

disulfide (p. 979)

disulfide bridge (p. 974)

Edman’s reagent (p. 984)

electrophoresis (p. 968)

b-pleated

endopeptidase (p. 985)

enzyme (p. 960)

essential amino acid (p. 963)

exopeptidase (p. 985)

fibrous protein (p. 982)

globular protein (p. 982)

(p. 989)

hydrophobic interactions (p. 992)

interchain disulfide bridge (p. 975)

intrachain disulfide bridge (p. 975)

ion-exchange chromatography(p. 970)

isoelectric point (p. 966)

kinetic resolution (p. 972)

loop conformation (p. 991)

N-terminal amino acid (p. 973)

oligomer (p. 993)

oligopeptide (p. 959)

paper chromatography (p. 969)

a-helix

parallel sheet (p. 990)

partial hydrolysis (p. 985)

peptide (p. 959)

peptide bond (p. 973)

sheet (p. 990)

polypeptide (p. 959)

primary structure (p. 982)

protein (p. 959)

quaternary structure (p. 982)

random coil (p. 994)

secondary structure (p. 982)

structural protein (p. 959)

subunit (p. 993)

tertiary structure (p. 982)

thin-layer chromatography (p. 969)

tripeptide (p. 959)

zwitterion (p. 965)

b-pleated

b-pleated

Problems

37. Unlike most amines and carboxylic acids, amino acids are insoluble in diethyl ether. Explain.


38. Indicate the peptides that would result from cleavage by the indicated reagent:
    a. His-Lys-Leu-Val-Glu-Pro-Arg-Ala-Gly-Ala by trypsin
    b. Leu-Gly-Ser-Met-Phe-Pro-Tyr-Gly-Val by chymotrypsin
    c. Val-Arg-Gly-Met-Arg-Ala-Ser by carboxypeptidase A
    d. Ser-Phe-Lys-Met-Pro-Ser-Ala-Asp by cyanogen bromide
    e. Arg-Ser-Pro-Lys-Lys-Ser-Glu-Gly by trypsin


39. Aspartame has a pI of 5.9. Draw its most prevalent form at physiological pH.


40. Draw the form of aspartic acid that predominates at
    a. b. c. d.


41. Dr. Kim S. Tree was preparing a manuscript for publication in which she reported that the pI of the tripeptide Lys-Lys-Lys was
    10.6. One of her students pointed out that there must be an error in her calculations because the of the group of lysine
    is 10.8 and the pI of the tripeptide has to be greater than any of its individual values. Was the student correct?


42. A mixture of amino acids that do not separate sufficiently when a single technique is used can often be separated by
    two-dimensional chromatography. In this technique, the mixture of amino acids is applied to a piece of filter paper and separated
    by chromatographic techniques. The paper is then rotated 90°, and the amino acids are further separated by electrophoresis,
    producing a type of chromatogram called a fingerprint. Identify the spots in the fingerprint obtained from a mixture of Ser, Glu,
    Leu, His, Met, and Thr.

Electrophoresis

at pH

=^5

Chromatography

−

+

pKa

pKa e-amino

pH=1.0 pH=2.6 pH=6.0 pH=11.0

Author: Insert term that is boldfacein text?

Or make lightface in text?

enkephalins (p. 976)

BRUI23-959-998r2 29-03-2003 1:37 PM Page 995