Chem 221 - Biochemistry for Science Majors » Fall 2021 » L4 Amino Acids and Proteins
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Question #1
The chirality of an amino acid results from the fact that its α carbon:
A.
is symmetric
B.
is in the L absolute configuration in naturally occurring proteins
C.
has no net charge
D.
is a carboxylic acid
E.
is bonded to four different chemical groups
Question #2
Amino acids are ampholytes because they can function as either a(n):
A.
transparent or a light-absorbing compound
B.
standard or a nonstandard monomer in proteins
C.
polar or a nonpolar molecule
D.
neutral molecule or an ion
E.
acid or a base
Question #3
Titration of valine by a strong base, for example NaOH, reveals two pK's. The titration reaction occurring at pK2 (pK2 = 9.62) is:
A.
—COOH + OH– → —COO– + H2O
B.
—NH3+ + OH– → —NH2 + H2O
C.
—COO– + —NH2+ → —COOH + —NH2
D.
—COOH + —NH2 → —COO– + —NH2+
E.
—NH2 + OH– → —NH– + H2O
Question #4
For amino acids with neutral R groups, at any pH below the pI of the amino acid, the population of amino acids in solution will have:
A.
no net charge
B.
no charged groups
C.
a net negative charge
D.
positive and negative charges in equal concentration
E.
a net positive charge
Question #5
The formation of a peptide bond between two amino acids is an example of a(n) ______________ reaction.
A.
group transfer
B.
isomerization
C.
oxidation reduction
D.
cleavage
E.
condensation
Question #6
At the isoelectric pH of a tetrapeptide:
A.
there are four ionic charges
B.
the total net charge is zero
C.
only the amino and carboxyl termini contribute charge
D.
the amino and carboxyl termini are not charged
E.
two internal amino acids of the tetrapeptide cannot have ionizable R groups
Question #7
A prosthetic group is:
A.
a fibrous region of a globular protein
B.
a subunit of an oligomeric protein
C.
a nonidentical subunit of a protein with many identical subunits
D.
synonymous with “protomer”
E.
a part of the protein that is not composed of amino acids
Question #8
Which one of the following amino acids contains an aromatic group?
A.
Methionine
B.
Leucine
C.
Glycine
D.
Arginine
E.
Phenylalanine
Question #9
An essential amino acid is one that
A.
the body cannot synthesize
B.
is essential to flagella motion
C.
is essentially easy to synthesize
D.
the body can synthesize under essential conditions
Question #10
Which of the following pairs of amino acids would carry a negative charge on their side chain at pH 8.0?
A.
Leucine & Glycine
B.
Asparagine & Glutamine
C.
Histidine & Lysine
D.
Aspartate & Glutamate
Question #11
How many different standard amino acids are there?
A.
20
B.
3
C.
100
D.
an infinite number
Question #12
Of the 20 standard amino acids, only ___________ is not optically active (nonchiral). The reason is that its side chain ___________.
A.
alanine; is a simple methyl group
B.
proline; forms a covalent bond with the amino group
C.
lysine; contains only nitrogen
D.
glycine; is unbranched
E.
glycine; is a hydrogen atom
Question #13
Which of the following is an amino acid?
A.
Proline
B.
Alanine
C.
Serine
D.
Glycine
Question #14
A protease
A.
is an enzyme that catalyzes proteolysis, the breakdown of proteins into smaller polypeptides or single amino acids
B.
increases the rate of proteolysis
C.
cleaves proteins by the addition of a molecule of water to a peptide bond
D.
is also called a peptidase or proteinase
E.
All the above statements are correct
Question #15
Proteases
A.
Produce amino acids or short peptides
B.
Cleave peptide bonds
C.
cleaves disulfide bonds
D.
Degrade proteins
E.
three of the choices are correct
Question #16
Chose the best true statement
A.
Proteases can cleave at specific points in the peptide chain
B.
Proteases are involved in many biological functions, including digestion of eaten proteins, and protein catabolism
C.
Proteases are involved in anabolism
D.
Two of the statement are incorrect
E.
Cleave all peptide bonds
Question #17
The fully protonated form of histidine has a ____________charge.
A.
+4
B.
+2
C.
+3
D.
+1
Question #18
Which of the following amino acids has a net negative charge at physiologic pH (~7.4)?
A.
Histidine
B.
Lysine
C.
Asparagine
D.
Glutamic Acid
Question #19
Based on the pKa values given in the attached table (see canvas tables), in there any amino acid among the ones in the list below that could serve as a buffer at pH 8.0?
A.
Tyrosine
B.
Cysteine
C.
Glutamic acid
D.
Histidine
E.
Leucine
Question #20
At pH = 0, the net charge on glutamic acid is:____________
A.
+2
B.
-1
C.
+1
D.
0
Question #21
At pH = 13, the net charge on lysine is:____________
A.
+3
B.
-1
C.
+2
D.
+1
Question #22
What is the charge of the dipeptide Ala-Lys a pH = 12?
A.
-1
B.
+1
C.
+2
D.
0
Question #23
The lowest charge possible for glutamic acid is
A.
-1
B.
-2
Question #24
The charge of cysteine at pH below 2 is
A.
0
B.
-1
C.
-2
D.
+1
Question #25
The charge of glutamic acid at pH > 10 is
A.
+2
B.
0
C.
+1
D.
-2
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