The net charge of the zwitterion form of Gly is ______.
K) zero
When a peptide bond is formed, an ______ reacts with a carboxylate group.
E) amino group
. At a pH above its pKa, the phenol group of tyrosine is ______.
deprotonated
. In the tripeptide Lys?Pro?Ile, there are ______ charged groups at pH 7
D) three
At a pH below its pKa, the -amino group of lysine is ______.
Ans: L
L) protonated
. At a pH below its pKa, the -carboxylate group of Asp is ______.
B) uncharged/L) protonated
. In the peptide Trp?Ser?Val, valine is at the ______.
G) C-terminus
In the tripeptide Trp?Val?Phe, the N-terminal residue is ______.
N) tryptophan
In the tripeptide Lys?Pro?Ile, the C-terminal residue is _________.
M) isoleucine
. Biological systems usually produce a single enantiomer, whereas chemical synthesis produces a ______.
I) racemic mixture
GABA is a neurotransmitter derived from ______.
A) glutamate
Glutathione is a tripeptide containing a central ______ residue.
J) cysteine
In the early 1930's William Rose fed laboratory rats a mixture of all 19 amino acids known to be present in proteins. He observed that his rats lost weight. This observation led to the discovery of ______ as the 20th amino acid found in proteins
E) Thr
. What percentage of the 20 amino acids is considered to be nutritionally essential to lab animals?
C) 50%
About half of the 20 amino acids are called essential because
E) our bodies cannot synthesize them and therefore they need to be present in our diet.
Which amino acid does not have a primary -amino group?
D) proline
17. Which of the following statements is true?
B) Purines and pyrimidines can be derived from amino acids.
. Which of the following amino acids is the least abundant in proteins
B) W
Zwitterions are
C) ions that bear both negatively and positively charged groups.
. The formation of a dipeptide from two amino acids involves
B) loss of water.
21
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Which of the following amino acids has a charged polar side chain at pH 7.0?
E) Glu
Which of the following tripeptides carries a net positive charge at pH 7.0?
E) Leu?Lys?Gly
Which of the following amino acids has a sulfur atom in its side chain?
D) Met
Which of the following amino acids does not have an ionizable side chain?
E) Asn
. Which of the following amino acids has an uncharged polar side chain at pH 7.0?
B) Thr
27
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. The ionization of amino acids depends on the pH and the pKas of the ionizable groups. The pK1 and pK2 for the amino acid shown above are 2.1 and 8.8, respectively. At what pH is the amino acid ionized predominantly as shown?
A) pH 1.0
The pK1, pK2, and pKR for the amino acid arginine are 1.8, 9.0, and 12.5, respectively. At pH 7.0 arginine would be charged predominantly as follows:
D) -carboxylate ?1, -amino +1, guanidino +1, net charge +1
. The pK1, pK2, and pKR for the amino acid aspartic acid are 2.0, 9.9, and 3.9, respectively. At pH 7.0, aspartic acid would be charged predominantly as follows:
B) -carboxylate ?1, -amino +1, -carboxylate ?1, net charge ?1
The pK1, pK2, and pKR for the amino acid glutamate are 2.1, 9.5, and 4.1, respectively. At pH 11.0, glutamate would be charged predominantly as follows:
E) -carboxylate ?1, -amino 0, -carboxylate ?1, net charge ?2
. The pK1, pK2, and pKR for the amino acid histidine are 1.8, 9.3, and 6.0, respectively. At pH 4.0 would be charged predominantly as follows:
D) -carboxylate ?1, -amino +1, imidazole +1, net charge +1
. The pK1, pK2, and pKR for the amino acid cysteine are 1.9, 10.7, and 8.4, respectively. At pH 5.0, cysteine would be charged predominantly as follows:
D) -carboxylate ?1, -amino +1, sulfhydryl 0, net charge 0
. The pK1, pK2, and pKR for the amino acid lysine are 2.2, 9.1, and 10.5, respectively. At pH 1.0, lysine would be charged predominantly as follows:
D) -carboxylate 0, -amino +1, -amino +1, net charge +2
35
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What is the name of the N-terminal amino acid in the peptide shown above?
B) methionine
What is the three-letter symbol for the C-terminal amino acid in the peptide shown above?
E) Phe
While proteins are usually composed of linear chains of amino acids, branched chains of amino acids and internally cross-linked chains can be found in certain proteins. Polypeptide chains are most commonly linked to each other through
D) disulfide bonds
The disulfide bond between two cysteine molecules
C) is a covalent bond formed by oxidation.
.40
...
41
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. The tripeptide glycylarginylglutamate contains four ionizable groups with pKas of 2.1, 4.1 9.8, and 12.5. Calculate the pI for this molecule.
C) 7.0
. The tripeptide alanyllysylaspartate contains four ionizable groups with pKas of 2.0, 3.9, 9.9, and 10.5. Calculate the pI for this molecule.
E) none of the above
The isoelectronic point of an amino acid is the point where
E) the amino acid carries no net electrical charge.
. The side-chains of amino acids have
D) different pKas in peptides as compared to the free amino acids
Asx refers to
D) either aspartic acid or asparagine.
The peptide AYDG has an N-terminal _________ residue.
E) alanine
. Which of the following tripeptides would be expected to be the most hydrophobic
C) GYA
. What is the three-letter abbreviation for the peptide valylarginylisoleucine?
A) Val?Arg?Ile
. Ribosomes use L amino acids to synthesize proteins. These amino acids are called "L" because
C) they have a configuration of groups around the C that can be related to the configuration of groups around the asymmetric carbon in L-glyceraldehyde
. Ribosomes use L amino acids to synthesize proteins. These amino acids are called "L" because
E) none of the above
Which of the amino acids represented below has two chiral centers?
C) Ile
53
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54/ All the standard amino acids except ____ are optically active.
A) Pro
) Gly
. The __________ character of most standard amino acids causes solutions of amino acids to rotate the plane of polarized light.
A) chiral
All amino acids derived from proteins have the same stereochemical conformation as.
A) L-glyceraldehyde.
. Typically, modified amino acids, those with side chain modifications that are present in proteins
C) are formed by modification of standard side chain residues after the protein is synthesized.
58. An amide bond between a side-chain carboxylate and an -amino group is also called a(n)
D) isopeptide bond.
What is the name of this molecule?
diagram
glutathione
. Residues 1 and 2 in the peptide shown above are connected through a
diagram
B) an isopeptide bond.
61. What is the three-letter symbol of the N-terminal amino acid in the structure shown above?
D) Glu
Glutamine is an amino acid (pKas are 2.2, and 9.1). Draw the predominant structure of glutamine at pH 1.0.
diagram
. Glutamic acid is an amino acid (pKas are 2.1, 4.1 and 9.5). Calculate the isoelectric point of glutamic acid.
: At pH 1.0 glutamic acid has an electric charge of +1, at pH 3.0 the electric charge equal 0, and at pH 5.0 the electric charge equals ?1. Therefore the pKas of the carboxylic acid groups surround the neutral form. pI = (2.1 + 4.1)/2 = 3.1
Tryptophan is an amino acid (pKas are 2.5, and 9.4).
a. How many different amino acids can be incorporated into proteins during translation?
b. Give the three- and one-letter abbreviation for tryptophan.
c. Draw the predominant structure of tryptophan at
a. 20
b. Trp and W
c. diagram
d. pI = (2.5 + 9.4)/2 = 6.0
. In general, amino acids are chiral molecules that act as building blocks for proteins. In addition, amino acids and amino acid derivative can act as extracellular messenger molecules such as hormones or neurotransmitters.
a. How many different amino aci
a. 20
b. L
c. glycine, glutamate, -aminobutyric acid (GABA), dopamine, or serotonin
d. diagram
. The figure below shows the predominant structure of an oligopeptide at pH 7.0.
diagram
a. How many amino acids are present in this peptide?
b. Circle one peptide bond in this peptide.
c. Draw a square around one alpha carbon in this peptide
d. The pKas
a. 5
b. diagram
c.
d. The charge of this molecule at pH 1.0 is +1. At pH 1.0 all ionizable groups are protonated; the two carboxylic acid groups are neutral and the amino group is positively charged.
e. aspartate (aspartic acid)
The picture below shows the structure of -amino-butyric acid (GABA).
a. From which amino acid is GABA derived (give the name of the amino acid closest in structure to GABA).
b. What is the structural difference between GABA and this amino acid.
c. What is
a. glutamate
b. GABA is missing the -carboxylic acid group
c. GABA is a neurotransmitter (a chemical that mediates communication between neurons)
The picture below shows the structure of serotonin.
diagram
a. From which amino acid is serotonin derived?
b. What are the structural differences between serotonin and this amino acid?
c. What is the function of serotonin?
d. Which illness can be caused b
a. Tryptophan
b. Serotonin has a hydroxyl group attached to the 6-membered ring and it misses the -amino group.
c. Serotonin is a neurotransmitter
d. Depression