Quiz Amino Acids, Peptides, Proteins Flashcards
The chirality of an amino acid results from the fact that its α carbon:
A) has no net charge.
B) is a carboxylic acid.
C) is bonded to four different chemical groups.
D) is in the L absolute configuration in naturally occurring proteins.
E) is symmetric.
C) is bonded to four different chemical groups.
Of the 20 standard amino acids, only ___________ is not optically active. The reason is that its side chain ___________.
A) alanine; is a simple methyl group
B) glycine; is a hydrogen atom
C) glycine; is unbranched
D) lysine; contains only nitrogen
E) proline; forms a covalent bond with the amino group
B) glycine; is a hydrogen atom
Two amino acids of the standard 20 contain sulfur atoms. They are: A) cysteine and serine. B) cysteine and threonine. C) methionine and cysteine D) methionine and serine E) threonine and serine.
C) methionine and cysteine
All of the amino acids that are found in proteins, except for proline, contain a(n): A) amino group. B) carbonyl group. C) carboxyl group. D) ester group. E) thiol group.
A) amino group.
Which of the following statements about cystine is correct?
A) Cystine forms when the —CH2—SH R group is oxidized to form a —CH2—S—S—CH2— disulfide bridge between two cysteines.
B) Cystine is an example of a nonstandard amino acid, derived by linking two standard amino acids.
C) Cystine is formed by the oxidation of the carboxylic acid group on cysteine.
D) Cystine is formed through a peptide linkage between two cysteines.
E) Two cystines are released when a —CH2—S—S—CH2— disulfide bridge is reduced to —CH2—
SH.
Cystine forms when the —CH2—SH R group is oxidized to form a —CH2—S—S—CH2— disulfide bridge between two cysteines.
Amino acids are ampholytes because they can function as either a(n):
A) acid or a base.
B) neutral molecule or an ion.
C) polar or a nonpolar molecule.
D) standard or a nonstandard monomer in proteins.
E) transparent or a light-absorbing compound.
A) acid or a base.
The formation of a peptide bond between two amino acids is an example of a(n) \_\_\_\_\_\_\_\_\_\_\_\_\_\_ reaction. A) cleavage B) condensation C) group transfer D) isomerization E) oxidation reduction
B) condensation
Which of the following is correct with respect to the amino acid composition of proteins?
A) Larger proteins have a more uniform distribution of amino acids than smaller proteins.
B) Proteins contain at least one each of the 20 different standard amino acids.
C) Proteins with different functions usually differ significantly in their amino acid composition.
D) Proteins with the same molecular weight have the same amino acid composition.
E) The average molecular weight of an amino acid in a protein increases with the size of the protein.
Proteins with different functions usually differ significantly in their amino acid composition.
Which of the following refers to particularly stable arrangements of amino acid residues in a protein that give rise to recurring patterns? A) Primary structure B) Secondary structure C) Tertiary structure D) Quaternary structure E) None of the above
Secondary structure
Which of the following describes the overall three-dimensional folding of a polypeptide? A) Primary structure B) Secondary structure C) Tertiary structure D) Quaternary structure E) None of the above
Quaternary structure
The term specific activity differs from the term activity in that specific activity:
A) is measured only under optimal conditions.
B) is the activity (enzyme units) in a milligram of protein.
C) is the activity (enzyme units) of a specific protein.
D) refers only to a purified protein.
E) refers to proteins other than enzymes.
is the activity (enzyme units) in a milligram of protein.
The functional differences, as well as differences in three-dimensional structures, between two different enzymes from E. coli result directly from their different: A) affinities for ATP. B) amino acid sequences. C) roles in DNA metabolism. D) roles in the metabolism of E. coli. E) secondary structures.
amino acid sequences.
One method used to prevent disulfide bond interference with protein sequencing procedures is:
A) cleaving proteins with proteases that specifically recognize disulfide bonds.
B) protecting the disulfide bridge against spontaneous reduction to cysteinyl sulfhydryl groups.
C) reducing disulfide bridges and preventing their re-formation by further modifying the —SH
groups.
D) removing cystines from protein sequences by proteolytic cleavage.
E) sequencing proteins that do not contain cysteinyl residues.
reducing disulfide bridges and preventing their re-formation by further modifying the —SH
groups.
All of the following are considered “weak” interactions in proteins, except: A) hydrogenbonds. B) hydrophobic interactions. C) ionic bonds. D) peptidebonds. E) van der Waals forces.
D) peptidebonds.
The most important contribution to the stability of a protein’s conformation appears to be the:
A) entropy increase from the decrease in ordered water molecules forming a solvent shell around it.
B) maximum entropy increase from ionic interactions between the ionized amino acids in a protein.
C) sum of free energies of formation of many weak interactions among the hundreds of amino acids
in a protein.
D) sum of free energies of formation of many weak interactions between its polar amino acids and
surrounding water.
E) stabilizing effect of hydrogen bonding between the carbonyl group of one peptide bond and the
amino group of another.
entropy increase from the decrease in ordered water molecules forming a solvent shell around it.
