What is the pH of a serine solution in which the ?-NH3+ group (pKa 9.2) is one-third dissociated?
8.9
Glutamic acid has pKas at 2.2, 4.3 and 9.7. Calculate the isoelectric point for glutamic acid.
3.25
If the pI of a peptide is 4.6, ___ might be present while ___ would probably be absent.
Glu, Lys
16. An amino acid + an aldehyde ? water + ?
Schiff base
The pKa of the cysteine side chain ________ group is 8.32, so it is about 11% dissociated at pH ______.
sulfhydryl, 7.4
Ninhydrin has all these properties EXCEPT:
a. It reacts with an amino acid by oxidatively deaminating its amino group.
b. It can be used to detect the location of amino acids following chromatography.
c. It produces a purple colored product upon reaction
D
All of the following react with the -SH group on cysteine EXCEPT:
a. N-ethylmaleimide.
b. iodoacetate.
c. acrylonitrile.
d. "Ellman's Reagent".
e. benzaldehyde.
e. benzaldehyde
Which of the peptides would absorb light at 280 nm?
ala-ala-trp
Which of the following amino acids absorbs light most strongly between 250 and 300 nm?
Trp
All are true for stereoisomers EXCEPT:
a. A diastereomer is a nonsuperimposable non-mirror image.
b. An enantiomer is a nonsuperimposable mirror image.
c. Diastereomers have different melting points.
d. Diastereomers rotate plane polarized light in equal
D
All are true statements about L-isoleucine EXCEPT:
a. Its enantiomer is named D-isoleucine.
b. L-alloleucine would be its diastereomer.
c. It contains a total of two asymmetric or chiral carbons.
d. It can also be named as (2S,3S)-isoleucine using the (R,
E
Using a cation exchange resin, a mixture of four amino acids is separated using an elution gradient of increasing NaCl solution. What would be the correct elution sequence?
asp, ser, lys, arg
The intrinsic properties of the 20 amino acids include all EXCEPT:
a. ?-Carbon is symmetric.
b. The capacity to polymerize.
c. Novel acid-base properties.
d. Varied structure and chemical functionality in side chains.
e. Chirality
A
The amino and carboxyl groups of amino acids react in a head-to-tail fashion, eliminating water, and forming a covalent _____ linkage typically referred to as a ____________ bond.
amide, peptide
Because peptide bond formation is thermodynamically ____________, biological systems must couple peptide bond formation to a thermodynamically ____________ reaction.
unfavorable, favorable
All of the statements about the classification of these amino acids are correct EXCEPT:
a. Aspartic acid and asparagine are acidic amino acids.
b. Alanine and valine are neutral, nonpolar amino acids.
c. Serine and glutamine are polar, uncharged amino aci
A
The difference between serine and homoserine is the same as between cysteine and homocysteine. This change from the common amino acid is:
one additional -CH2- group.
Which of the following amino acids has more than one chiral carbon?
threonine
Which of the listed amino acids is classified as a basic amino acid?
a. leucine
b. phenylalanine
c. aspartate
d. asparagine
e. lysine
E. lysine
All of the amino acids EXCEPT _________ have both free ?-amino and free ?-carboxyl groups.
a. aspartic acid
b. proline
c. asparagine
d. lysine
e. valine
b. proline
The amino acid with a side-chain pKa near neutrality and which therefore plays an important role as proton donor and acceptor in many enzyme catalyzed reactions is:
histidine
10. The pKa of the ?-NH3+ group is ___________ by the presence on an amino acid by the ? -COO- group.
slightly decreased (~ 1.5 pH units)
Which statement is INCORRECT about these amino acids, and amino acid derivatives?
a. GABA (?-aminobutyric acid) is a potent inhibitory neurotransmitter derived from glutamic acid.
b. Ornithine is an important metabolic intermediate.
c. Epinephrine is a ho
C
At which of the following pH values would histidine (pKa values of 1.8, 6.0 and 9.2) be found with a net negative charge?
11
When using a strongly acidic polystyrene resin (Dowex-50) chromatography column, the separation is PRIMARILY by
ion exchange chromatography.