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?
11.0
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
When using a strongly acidic polystyrene resin (Dowex-50) chromatography column, the separation is PRIMARILY by
ion exchange chromatography.