Ch03 - Amino Acids and Peptides Flashcards
The amino and carboxyl groups of amino acids are bonded to which carbon?
a. Both are bonded to the α-carbon.
b. Both are bonded to the β-carbon.
c. The amino is bonded to the α-carbon, and the carboxyl is bonded to the β-carbon.
d. The amino is bonded to the β-carbon, and the carboxyl is bonded to the α-carbon.
a. Both are bonded to the α-carbon.
The side chain groups of amino acids are bonded to which carbon?
a. The α-carbon.
b. The β-carbon.
c. The carbonyl carbon.
d. Different amino acids have their side chains attached to different carbons
a. The α-carbon.
Chiral objects
a. are cyclic compounds in the chair form.
b. are not superimposable on their mirror images.
c. never occur in nature.
d. do not form crystals.
b. are not superimposable on their mirror images.
Which of the following has no L or D configuration?
a. Glyceraldehyde
b. Proline
c. Glycine
d. All of these have an L or D configuration
c. Glycine
The absolute configuration of amino acids are denoted by their relationship to the L- or D- forms of
a. glyceraldehyde
b. glucose
c. tartaric acid
d. alanine
a. glyceraldehyde
The amino acids which occur in proteins
a. are all of the L- form.
b. are all of the D- form.
c. can be either the L- or D- form.
d. do not have L- and D- forms.
a. are all of the L- form.
Which of the following is an amino acid not found in proteins?
a. asparagine
b. ornithine
c. isoleucine
d. proline
b. ornithine
Which amino acid has the one-letter symbol E?
a. lysine
b. phenylalanine
c. histidine
d. glutamic acid
d. glutamic acid
Which amino acid has the three-letter symbol asn?
a. aspartic acid
b. asparagine
c. alanine
d. arginine
b. asparagine
Which is a correct pair of abbreviations for an amino acid?
a. Gln / N
b. Tyr / T
c. Asn / N
d. Phe / P
e. Pro / Q
c. Asn / N
Which amino acid has a benzene-like ring?
a. Glutamic Acid
b. Histidine
c. Isoleucine
d. Serine
e. Tyrosine
e. Tyrosine
Which amino acid is classified as polar?
a. L
b. H
c. P
d. I
b. H
Which group consists only of amino acids with polar side chains?
a. serine, threonine, and leucine
b. serine, threonine, and cysteine
c. serine, threonine, and valine
d. serine, threonine, and isoleucine
b. serine, threonine, and cysteine
Which of the following has a hydrophilic side chain?
a. Asn
b. Leu
c. Ile
d. Gly
a. Asn
Which of the following amino acids has a side chain that can make hydrogen bonds to other molecules?
a. Leu
b. Ser
c. Ala
d. Gly
b. Ser
Asp and Glu both have amides as side chains.
a. True
b. False
b. False
Thr and Ser both have hydroxyls as side chains.
a. True
b. False
a. True
The side chain of Met is a poor hydrogen bond donor.
a. True
b. False
a. True
Which group consists only of amino acids with carboxylate side chains?
a. glutamate and cysteine
b. aspartate and glycine
c. glutamate and lysine
d. aspartate and glutamate
d. aspartate and glutamate
Which group consists only of amino acids with basic side chains?
a. leucine and lysine
b. arginine and leucine
c. lysine and arginine
d. arginine and isoleucine
c. lysine and arginine
Which amino acids contain sulfur?
a. cysteine and lysine
b. cysteine and methionine
c. arginine and methionine
d. cysteine and isoleucine
b. cysteine and methionine
Which amino acid takes on a negative charge when the R-group loses a proton?
a. Glutamic Acid
b. Histidine
c. Glutamine
d. Tyrosine
e. Glutamic Acid and Tyrosine
e. Glutamic Acid and Tyrosine
Which amino acid takes on a positive charge when the R-group gains a proton?
a. Glutamic Acid
b. Histidine
c. Glutamine
d. Tyrosine
e. Glycine
b. Histidine
Given the R-groups in the peptide, ALA-GLN-ARG-SER-HIS, it would likely be:
a. Very water soluble
b. Somewhat water soluble
c. Not very water soluble
d. Not soluble at all
e. You cannot tell from the sequence
a. Very water soluble
Which is the correct one-letter designation for tryptophan?
a. E
b. T
c. W
d. Q
e. none of the choices
c. W
Which amino acid has a polar, non-ionic R-group
a. Glutamic Acid
b. Histidine
c. Isoleucine
d. Serine
e. Tyrosine
d. Serine
Which amino acid has the least polar R-group H?
a. Glutamic Acid
b. Histidine
c. Isoleucine
d. Serine
e. Tyrosine
c. Isoleucine
Which amino acid would have the greatest negative charge at pH = 7.0?
a. Glutamic Acid
b. Histidine
c. Isoleucine
d. Serine
e. Tyrosine
a. Glutamic Acid
Which amino acid would likely be least water-soluble at pH 7.0?
a. Histidine
b. Isoleucine
c. Isoleucine or Tyrosine, you cannot tell
d. Serine
e. Tyrosine
c. Isoleucine or Tyrosine, you cannot tell
Which of the following is NOT a correct combination of an amino acid, its three-letter designation, and its one-letter designation?
a. Lysine, lys, L
b. Glycine, gly, G
c. Histidine, his, H
d. Tryptophan, Trp, W
e. Arginine, arg, R
a. Lysine, lys, L
Which of the following is not considered an uncommon amino acid?
a. thyroxine
b. Hydroxylysine
c. Hydroxyproline
d. Tryptophan
d. Tryptophan
Which statement is true about the classification of amino acids?
a. Alanine and valine are basic amino acids.
b. Lysine and arginine are acidic amino acids.
c. Glutamic acid and asparagine are hydrophobic amino acids.
d. Tryptophan and phenylalanine are aromatic amino acids.
e. Methionine and cysteine are hydroxyl-containing amino acids.
d. Tryptophan and phenylalanine are aromatic amino acids.
Which amino acid has a basic R group?
a. Glutamic Acid
b. Histidine
c. Isoleucine
d. Serine
e. Tyrosine
b. Histidine
Which of the following is true about uncommon amino acids?
a. They are found in all proteins
b. When they are found in proteins, they are first created by modification of the parent amino acid and then
incorporated into the protein
c. They are formed in the protein by post-translational modification of the parent amino acid
d. They are always based on modification of tyrosine
e. none of the choices
c. They are formed in the protein by post-translational modification of the parent amino acid
Which of the following can be considered a unique characteristic of histidine?
a. Its side chain is attached to the alpha carbon
b. It has a basic side chain
c. It has a side chain that is chemically basic but has an acidic pKa
d. It is technically an “imino” acid
c. It has a side chain that is chemically basic but has an acidic pKa
Which amino acids would migrate furthest toward the anode (positive electrode) during electrophoresis?
a. Aspartic acid.
b. Arginine.
c. Tyrosine.
d. Histidine.
e. Glutamine.
a. Aspartic acid.
What is the charge on the tetrapeptide lys-lys-his-glu at pH 7?
a. 0
b. +1
c. +2
d. −1
b. +1
The pKa values of the alpha carboxyl groups of common amino acids are around
a. pH 2
b. pH 5
c. pH 7
d. pH 9
a. pH 2
The pKa values of the side chains of the common amino acids
a. are always at low pH
b. are always at high pH
c. depend on the chemical nature of the side chain
d. are not known
c. depend on the chemical nature of the side chain
The pKa values of the amino groups of common amino acids
a. occur at very low pH values
b. occur in a range from pH 9 to pH 11
c. all occur at pH 8
d. all occur above pH 12
b. occur in a range from pH 9 to pH 11
The isoelectric pH of glycine is closest to
a. pH 4
b. pH 6
c. pH 8
d. pH 10
b. pH 6
Which of the following correctly lists the isoelectric pH’s of asp, asn, and arg from lowest to highest?
a. D N R
b. D R N
c. R N D
d. R D N
e. N R D
f. N D R
a. D N R
Which of the following amino acids has a net charge of +1 at pH 4 and a net charge of 0 at pH 8?
a. glu
b. arg
c. his
d. tyr
c. his
The net charge on the amino acid cys in a solution at pH 7 is closest to
a. −2
b. −1.
c. 0.
d. +1.
c. 0.
What is the predominant form of the amino acid abbreviated R at pH 7?
a. positive
b. neutral
c. negative
a. positive
What is the predominant form of the amino acid abbreviated val at pH 7?
a. positive
b. neutral
c. negative
b. neutral
What is the predominant form of the amino acid abbreviated E at pH 7?
a. positive
b. neutral
c. negative
c. negative
Refer to Exhibit 3A. At pH 7, what percent of histidine has a neutral charge?
a. 9%
b. 50%
c. 91%
d. 100%
c. 91%
Refer to Exhibit 3A. The pI of an amino acid is the pH at which it has a zero net charge. What is the increasing order of isoelectric points (low pH to high) for these three amino acids?
a. ALA, HIS, ASP
b. ASP, ALA, HIS
c. HIS, ALA, ASP
d. ALA, ASL, HIS
e. ASP, HIS, ALA
b. ASP, ALA, HIS
Refer to Exhibit 3A. Which of these amino acids could act as a good buffer at pH = 4.5
a. Alanine
b. Arginine
c. Asparagine
d. Cysteine
e. Aspartic Acid
e. Aspartic Acid
Refer to Exhibit 3A. Which one has the R-group with the highest pK?
a. Alanine
b. Arginine
c. Histidine
d. Cysteine
e. Aspartic Acid
b. Arginine
Refer to Exhibit 3A. Calculate the pI of ASN:
a. 2.5
b. 5.0
c. 5.5
d. 6.0
e. 10.7
c. 5.5
Refer to Exhibit 3A. What is the order of the pIs in increasing order (from acid to base)?
a. Alanine, Arginine, Asparagine, Cysteine, and Aspartic Acid
b. Aspartic Acid, Alanine, Asparagine, Cysteine, and Arginine
c. Aspartic Acid, Cysteine, Asparagine, Alanine, and Arginine
d. Arginine, Alanine, Asparagine, Cysteine, and Aspartic Acid
e. Aspartic Acid, Cysteine, Arginine, Alanine, and Asparagine,
c. Aspartic Acid, Cysteine, Asparagine, Alanine, and Arginine
Refer to Exhibit 3A. Which one has a pI of 5.0?
a. Alanine
b. Arginine
c. Histidine
d. Cysteine
e. Glutamic acid
d. Cysteine
Refer to Exhibit 3A. Calculate the pI of CYS?
a. 1.7
b. 5.0
c. 8.3
d. 9.6
e. 10.8
b. 5.0
Refer to Exhibit 3A. The pI of the peptide ALA-GLN-ARG-SER-HIS would be:
a. Strongly acid
b. Weakly acid (4-6)
c. About neutral (6-8)
d. Weakly basic (8-10)
e. Strongly basic
d. Weakly basic (8-10)
At its isoelectric pH, glycine will have
a. both of its ionizable functional groups dissociated.
b. neither of its ionizable functional groups dissociated.
c. only its carboxyl group dissociated.
d. only its amino group dissociated.
a. both of its ionizable functional groups dissociated.
The net charge on the peptide abbreviated CAKE in a solution at pH 7 is closest to
a. −2
b. −1.
c. 0.
d. +1.
c. 0.
Refer to Exhibit 3B. Which points on the graph represent pK’s?
a. 1 and 7
b. 2, 4 and 6
c. 3 and 5
d. 2, 3, 4, 5 and 6
e. The pKs cannot be determined without more information.
b. 2, 4 and 6
Refer to Exhibit 3B. Which point most likely represents the pK for the carboxyl group?
a. 1
b. 2
c. 3
d. 4
e. 5
b. 2
Refer to Exhibit 3B. At which point would the amino acid have its maximum negative charge?
a. 1
b. 2
c. 4
d. 6
e. 7
e. 7
Refer to Exhibit 3B. The amino acid depicted by the titration curve is
a. aspartic acid
b. histidine
c. lysine
d. tyrosine
e. lysine or tyrosine
e. lysine or tyrosine
Refer to Exhibit 3B. The point labeled #1 represents:
a. The fully protonated form
b. The pH with maximum negative charge
c. The end point of titration with base (OH−)
d. The pI of the amino acid
e. None of these
d. The pI of the amino acid
Which of the following correctly describes peptide bonds?
a. They are special type of amide bond.
b. They are a very stable bonds.
c. They are formed when water is split out from an amino group and a carboxylic acid.
d. They are a bond which displays resonance.
e. All of these
e. All of these
How many possible tetrapeptides can be made using all four of the amino acids D, W, F, and R?
a. 4
b. 6
c. 12
d. 24
e. none of the choices
d. 24
This amino acid displays a free amino group in the peptide ALA-GLN-ARG-SER-HIS:
a. ALA
b. GLN
c. SER
d. HIS
a. ALA
How many different tripeptides can be assembled using one molecule each of the amino acids glycine, glutamic acid, and lysine?
a. 3
b. 6
c. 9
d. 27
b. 6
Which groups of a pair of amino acids must react to form a peptide bond?
a. the two carboxyls
b. the two aminos
c. the two R-groups
d. the carboxyl of one and the amino of the other
d. the carboxyl of one and the amino of the other
Which is the C-terminal amino acid in the peptide ALA-GLN-ARG-SER-HIS?
a. ALA
b. GLN
c. ARG
d. SER
e. HIS
e. HIS
The peptide bond
a. is formed by elimination of water between two amino groups in an amindo acid
b. limits the possible orientations of the peptide backbone in a protein
c. has acidic and basic characteristics
d. all of these
b. limits the possible orientations of the peptide backbone in a protein
The peptide bond
a. is planar
b. can be written as a resonance hybrid
c. is the basis of protein structure.
d. all of the above
d. all of the above
The order in which amino acids are linked in peptides is given
a. from the C-terminal to the N-terminal end
b. from the N-terminal to the C-terminal end
c. in alphabetical order
d. in order of increasing molecular weights of the amino acid residues
b. from the N-terminal to the C-terminal end
Oxytocin and vasopressin
a. differ from each other by a single amino acid
b. do not contain sulfur
c. are peptide hormones
d. are tripeptides
c. are peptide hormones
Which of the following is true about oxytocin?
a. it is a peptide hormone
b. during pregnancy the number of receptors for oxytocin increases
c. it is involved in stimulating the flow of milk during nursing
d. all of the choices
d. all of the choices
Which of the following is the most similar between oxytocin and vasopressin?
a. their biological function
b. their amino acid sequences
c. their isoelectric point
d. their overall structure
d. their overall structure
What do amino acids such as alanine, leucine, isoleucine, tryptophan, and valine have in common?
a. They all are polar-neutral amino acids.
b. They all are nonpolar amino acids.
c. They all are acidic amino acids.
d. They all are basic amino acids.
b. They all are nonpolar amino acids.
Which of the following types of amino acids has uncharged side chains at neutral pH?
a. Nonpolar amino acids
b. Acidic amino acids
c. Polar-neutral amino acids
d. Basic amino acids
c. Polar-neutral amino acids
The method for separating molecules on the basis of the ratio of their charge to size is called _____.
a. electrolysis
b. electrophoresis
c. electroplating
d. electroporation
b. electrophoresis
Explain how thyroxine differs from its parent amino acid, tyrosine.
Thyroxine differs from tyrosine in a way that it has an extra iodine-containing aromatic group on the side chain; it is produced only in the thyroid gland, formed by posttranslational modification of tyrosine residues in the protein thyroglobulin. Thyroxin is then released as a hormone by proteolysis of thyroglobulin.
Which of the following statements is true of resonance structures?
a. Resonance structures differ from one another only in the positioning of electrons.
b. Resonance structures differ from one another only in the number of electrons.
c. Two resonance structures will always have the same number of single bonds and double bonds.
d. Two resonance structures will always have single bonds and double bonds in the same position.
a. Resonance structures differ from one another only in the positioning of electrons.
