chapter 4 - amino acids
What's the net charge of the peptide AEGK at physiological pH? +1 +2 +1 +2 0
0
In the tripeptide Lys-Pro-Ile, there are ____ charged groups at pH 7.
three
Amino acid derivatives play an important role in various biological processes. True False
true
The 20 standard amino acids are all optically active with the exception of glycine. False True
true
The net charge of the zwitterion form of Gly is
zero
Which of the following is the approximate net charge of aspartate at pH 12? -1 0 +2 +1 -2
-2
he 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: -carboxylate -1, -amino +1, guanidino +1, net charge +1 -carboxylate +1, -amino 0, guanidino -1, net charge 0 -carboxylate 0, -amino 0, guanidino +1, net charge +1 -carboxylate +1, -amino -1, guanidino -1, net charge -1 -carboxylate -1, -amino 0, guanidino +1, net charge 0
-carboxylate -1, -amino +1, guanidino +1, net charge +1
What is the pI of histidine? (Hint: Histidine has 3 pKa's) 5.50 6.0 7.59 9.17 3.91
7.59
Which of the following amino acids does not have an ionizable side chain? Asp Cys Lys His Asn
Asn
Some key points in the titration curve of an amino acid are labeled with the letters A to G. Identify the point(s) at which the amino acid would be a good buffer.
BDF at the mid points
Why is Gly considered achiral? Because Gly is the smallest amino acid. Because Gly has four different substituents attached to the carbon atom. Because Gly is normally found exposed on the protein surface. Because Gly's sidechain is a H atom.
Because Gly's sidechain is a H atom.
In the peptide Trp-Ser-Val, valine is at the
C-terminus
Which of the following tripeptides would be expected to be the most hydrophobic? KYG KYA GYA DYA DYG
GYA
Which of the following amino acid side chains are charged at physiological pH? Gln, Asn, Lys, and Arg Glu, Asp, Lys, and Arg Glu, Asp, Lys, Arg, and His Lys, His, and Arg
Glu, Asp, Lys, and Arg
There are several amino acid side chains which are always charged at physiological pH. These are: Glu, Asp, Lys, and His. Gln, Asn, Glu, and Asp. Glu, Lys, Asp, His, and Arg. Glu, Asp, Lys, and Arg. none of the above.
Glu, Asp, Lys, and Arg.
Which statement is FALSE about the classification of amino acids? Alanine and valine are hydrophobic amino acids. Threonine and glutamine are polar amino acids. Methionine and cysteine are sulfur-containing amino acids. Glutamic acid and asparagine are negatively charged amino acids. Lysine and arginine are positively charged amino acids.
Glutamic acid and asparagine are negatively charged amino acids.
Which of the amino acids represented below has two chiral centers? Ala Leu Ile Pro Asn
Ile
Typically, modified amino acids, those with side chain modifications that are present in proteins are synthesized due to genetic mutations. are assembled by specialized bacterial enzymes. are formed by modification of standard side chain residues after the protein is synthesized. are toxic. are racemic.
are formed by modification of standard side chain residues after the protein is synthesized.
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: -carboxylate 0, -amino 0, sulfhydryl 0, net charge 0 -carboxylate +1, -amino —1, sulfhydryl —1, net charge —1 -carboxylate —1, -amino +1, sulfhydryl +1, net charge +1 -carboxylate —1, -amino +1, sulfhydryl 0, net charge 0 -carboxylate +1, -amino —1, sulfhydryl 0, net charge 0
carboxylate —1, -amino +1, sulfhydryl 0, net charge 0
Which of the following amino acids has a side chain that can form covalent cross-links in proteins? Cysteine Tryptophan Threonine Methionine Serine
cysteine
which amino acid side chain forms disulfide bonds? Cysteine Methionine Histidine Lysine
cysteine
Which of the following amino acids has a charged polar side chain at pH 7.0? Leu Ala Met Trp Glu
glu
Which of the following tripeptides carries a net positive charge at pH 7.0? Ala-Thr-Asn Gln-Val-Ser Arg-Glu-Met Pro-Ile-Leu Leu-Lys-Gly
ley-lys-gly
The formation of a dipeptide from two amino acids involves loss of water. reduction of the α-carbon. oxidation of the α-carbon. side-chain complementarity. base catalysis.
loss of water.
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. 3.0 6.0 6.2 10.2 none of the above
none
Which amino acid does not have a primary -amino group? glutamine arginine lysine proline glutamate
proline
Which amino acid side chain is the least flexible? Lysine Leucine Proline Methionine
proline due to the ring
A _____ mixture contains equal amounts of each enantiomer.
racemic
The isoelectronic point of an amino acid is the point where the pKa of the -carboxylic acid is the same as the pKa of the -amino group. the -carboxylic acid is protonated and the -amino group is unprotonated. the solubility of the amino acid is maximized. the -carboxylic acid and the -amino group are both half protonated. the amino acid carries no net electrical charge.
the amino acid carries no net electrical charge.
Ribosomes use L amino acids to synthesize proteins.These amino acids are called "L" because they are chiral. they turn polarized light to the left. 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. they are all (S)-amino acids. they are all (R)-amino acids.
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.
Which of the following amino acid side chains is polar and uncharged? Tyr Ile Glu Phe Trp
tyr
Three of the 20 amino acids that are incorporated into proteins are aromatic. They are: tryptophan, phenylalanine, and proline. tyrosine, phenylalanine, and proline. valine, leucine, and isoleucine. tyrosine, phenylalanine, and tryptophan. arginine, lysine, and histidine.
tyrosine, phenylalanine, and tryptophan.
