-Plays a role in cellular metabolism.
-An iodine-containing thyroid hormone.
-Neurotransmitter.
-Mediator of allergic reactions.
-An iodine-containing thyroid hormone.
The Fischer convention is well suited for describing molecules with multiple chiral centers.
True or False ?
False , Fischer convention is best suited for describing molecules with one chiral center.
Lysine has pK values of 2.16, 9.06, and 10.54, for its carboxyl, -amino, and -amino groups, respectively. What is its estimated pI?
-9.06
-9.80
-6.85
-5.66
9.80
Which amino acid side chain is considered nonpolar?
Glutamine
Histidine
Isoleucine
Tyrosine
Isoleucine
Which amino acid side chain can form a hydrogen bond?
Isoleucine
Alanine
Glycine
Threonine
Threonine
Methionine is the only amino acid that contains sulfur.
False or True ?
False , methionine and cysteine both have Sulfur groups
By convention the amino terminal residue of a peptide chain is written as the right-most residue.
True or False ?
False , N-terminus is the left most and C-terminus is the right most.
The alpha-amino groups of all amino acids have a charge (+ or -) at pH 7.
positive (+)
The polymerization of amino acids to form a polypeptide can be represented as a ______ reaction.
condensation
_______ is the only amino acid of the 20 standard amino acids that lacks a primary amine.
proline
Aspartic Acid
Side chain is -CH2-SH.
Side chain is -CH2COOH.
Side chain is -CH3.
Side chain is -CH2OH.
Side chain is -H.
Side chain is -CH2-phenyl.
Side chain is -CH2-CH2-S-CH3.
Side chain is -CH2-CH2-CH2-CH2-NH2.
Side chain is -CH2COOH.
Serine
Side chain is -CH2COOH.
Side chain is -CH2-phenyl.
Side chain is -CH2-CH2-CH2-CH2-NH2.
Side chain is -CH2OH.
Side chain is -CH3.
Side chain is -CH2-CH2-S-CH3.
Side chain is -H.
Side chain is -CH2-SH.
Side chain is -CH2OH.
Methionine
Side chain is -CH3.
Side chain is -CH2-SH.
Side chain is -CH2-phenyl.
Side chain is -CH2OH.
Side chain is -CH2-CH2-CH2-CH2-NH2.
Side chain is -CH2-CH2-S-CH3.
Side chain is -H.Side chain is -CH2COOH
Side chain is -CH2-CH2-S-CH3.
Identify the side chain of each item listed:Glycine
Side chain is -CH2-phenyl.
Side chain is -H.
Side chain is -CH2COOH.
Side chain is -CH2-SH.
Side chain is -CH2OH.
Side chain is -CH3.
Side chain is -CH2-CH2-S-CH3.
Side chain is -CH2-CH2-CH2-CH2-NH2
Side chain is -H.
Molecules that are nonsuperimposable mirror images are known as _________ of each other.
diastereomers
enantiomers
zwitterions
racemers
enantiomers
What is the net overall charge on glutamic acid at pH 12.
-2
What is the net charge on the amino acid lysine at pH 7.
+1
The Fischer convention is commonly used to describe the stereochemistry of amino acids. In the Fischer convention, the configuration of the groups around an asymmetric center is compared to that of glyceraldehyde, a molecule with one asymmetric center. For e.g., L-glyceraldehyde and L-amino acids are said to have the same relative configuration.
True or False ?
True
Many drugs are chemically synthesized as racemic mixtures, although only one enantiomer has biological activity.
True or False ?
True
Proline can be modified by the addition of a hydroxy group.
True or False ?
True
Most peptides containing D-amino acids are not synthesized by the standard protein synthetic machinery.
True or False ?
True
A tripeptide that helps inactivate oxidative compounds is
glutathione
Some types of nonstandard amino acids are not generally found in polypeptides.
True or False ?
True
Modification of amino acids in proteins is rarely important for function.
True or False ?
False
All standard amino acids except glycine have one asymmetric carbon.
False or True ?
False , All standard amino acids except glycine have one or more asymmetric carbons. Isoleucine and threonine have two asymmetric carbons.
D-amino acids are found in the short polypeptides of some _____ cell walls.
bacterial
All standard amino acids, except _______ have a chiral alpha carbon
glycine
Why is the pK of the carboxyl group of glycine (2.35) so much lower than that of acetic acid (4.76)?
Because the positively-charged amino group of glycine stabilizes the carboxylate group
Glutamic acid has pK values of 2.10, 4.07, and 9.47 for its -carboxyl group, -carboxyl group, and -amino group, respectively. What is its estimated pI?
5.785
3.085
4.07
6.77
3.085
Glutamine has pK values of 2.17 and 9.13. What is its estimated pI?
2.17
5.65
7.00
9.13
5.65
Which amino acid side chain is the least flexible?
Leucine
Lysine
Proline
Methionine
Proline
Which amino acid side chain is most likely to be positively charged at pH 7?
Serine
Tyrosine
Arginine
Aspartic acid
Arginine
Which amino acid side chain is considered polar?
Serine
Valine
Phenylalanine
Methionine
Serine
Glutamine can be converted into which amino acid by acid hydrolysis?
Glutamic acid
Asparagine
Arginine
Aspartic acid
Glutamic acid
Which amino acid side chain forms disulfide bonds?
Histidine
Lysine
Cysteine
Methionine
Cysteine
Which amino acid side chain is aromatic?
Alanine
Phenylalanine
Threonine
Glutamic acid
Phenylalanine
Which amino acid side chain cannot ionize?
Histidine
Aspartic acid
Asparagine
Cysteine
Asparagine
Which amino acid side chain cannot form a hydrogen bond?
Tryptophan
Glutamine
Valine
Tyrosine
Valine
The pI of any amino acid can be estimated by the average of the pK values of the -amino group and the -carboxyl group.
True or False ?
False
Almost all amino acids have ionizable side chains.
True or False ?
False
Leucine and alanine have large, nonpolar side chains.
True or False ?
False
Serine and valine have polar, uncharged side chains.
True or False ?
False
The condensation of two amino acids yields a peptide and a molecule of water.
False or True ?
True
By convention, polypeptide chains are named from left to right beginning with the amino acid at the (N or C ) -terminus.
N
The carboxylic groups of all amino acids have a_______ charge at pH 7.
negative
The_______ point is the pH at which a molecule has no net charge.
isoelectric
Amino acids that are incorporated into a polypeptide chain are referred to as amino acid _______
residues
Tryptophan
Side chain contains phenol group.
Side chain contains indole group.
Side chain contains guanidino group.
Side chain contains isopropyl group.
Side chain contains imidazole group.
Side chain contains sulfhydryl group.
Indole
Valine
Side chain contains indole group.
Side chain contains imidazole group.
Side chain contains guanidino group.
Side chain contains sulfhydryl group.
Side chain contains phenol group.
Side chain contains isopropyl group.
isopropyl group
Tyrosine
Side chain contains guanidino group.
Side chain contains sulfhydryl group.
Side chain contains isopropyl group.
Side chain contains phenol group.
Side chain contains imidazole group.
Side chain contains indole group
phenol group
Cysteine
Side chain contains isopropyl group.
Side chain contains phenol group.
Side chain contains imidazole group.
Side chain contains indole group.
Side chain contains guanidino group.
Side chain contains sulfhydryl group.
Side chain contains sulfhydryl group.
Arginine
Side chain contains imidazole group.
Side chain contains indole group.
Side chain contains guanidino group.
Side chain contains sulfhydryl group.
Side chain contains phenol group.
Side chain contains isopropyl group.
guanidino group
Histidine
Side chain contains indole group.
Side chain contains isopropyl group.
Side chain contains imidazole group.
Side chain contains guanidino group.
Side chain contains sulfhydryl group.
Side chain contains phenol group.
Imidazole group
How many functional groups does the peptide MDFGRKCDE have that can be titrated?
5
7
8
6
8
Which amino acid(s) could be used to make a buffer at pH 4.0?
Asp
Gln
Glu
Asp and Gln
Asp and Glu
Asp and Glu
Which of the 20 standard amino acids is not optically active (chiral) and why?
Glycine, because its side chain is a hydrogen atom.
How many charged groups do ALL isolated amino acids have at physiological pH?
1
more than 1
more than 2
Not all amino acids are charged
more than 1
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.
