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.
has no net charge
B.
is a carboxylic acid
C.
is symmetric
D.
is in the L absolute configuration in naturally occurring proteins
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.
polar or a nonpolar molecule
C.
standard or a nonstandard monomer in proteins
D.
acid or a base
E.
neutral molecule or an ion
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.
—NH2 + OH– → —NH– + H2O
D.
—COOH + —NH2 → —COO– + —NH2+
E.
—COO– + —NH2+ → —COOH + —NH2
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 charged groups
B.
a net negative charge
C.
a net positive charge
D.
positive and negative charges in equal concentration
E.
no net charge
Question #5
The formation of a peptide bond between two amino acids is an example of a(n) ______________ reaction.
A.
cleavage
B.
group transfer
C.
oxidation reduction
D.
condensation
E.
isomerization
Question #6
At the isoelectric pH of a tetrapeptide:
A.
the total net charge is zero
B.
two internal amino acids of the tetrapeptide cannot have ionizable R groups
C.
the amino and carboxyl termini are not charged
D.
there are four ionic charges
E.
only the amino and carboxyl termini contribute charge
Question #7
A prosthetic group is:
A.
synonymous with “protomer”
B.
a fibrous region of a globular protein
C.
a nonidentical subunit of a protein with many identical subunits
D.
a part of the protein that is not composed of amino acids
E.
a subunit of an oligomeric protein
Question #8
Which one of the following amino acids contains an aromatic group?
A.
Phenylalanine
B.
Methionine
C.
Arginine
D.
Leucine
E.
Glycine
Question #9
An essential amino acid is one that
A.
the body can synthesize under essential conditions
B.
is essentially easy to synthesize
C.
the body cannot synthesize
D.
is essential to flagella motion
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.
Aspartate & Glutamate
C.
Histidine & Lysine
D.
Asparagine & Glutamine
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.
glycine; is a hydrogen atom
B.
glycine; is unbranched
C.
lysine; contains only nitrogen
D.
proline; forms a covalent bond with the amino group
E.
alanine; is a simple methyl group
Question #13
Which of the following is an amino acid?
A.
Serine
B.
Glycine
C.
Alanine
D.
Proline
Question #14
A protease
A.
increases the rate of proteolysis
B.
is also called a peptidase or proteinase
C.
is an enzyme that catalyzes proteolysis, the breakdown of proteins into smaller polypeptides or single amino acids
D.
cleaves proteins by the addition of a molecule of water to a peptide bond
E.
All the above statements are correct
Question #15
Proteases
A.
Produce amino acids or short peptides
B.
Cleave peptide bonds
C.
Degrade proteins
D.
cleaves disulfide bonds
E.
three of the choices are correct
Question #16
Chose the best true statement
A.
Proteases are involved in anabolism
B.
Two of the statement are incorrect
C.
Proteases can cleave at specific points in the peptide chain
D.
Proteases are involved in many biological functions, including digestion of eaten proteins, and protein catabolism
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.
Lysine
B.
Histidine
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.
Glutamic acid
C.
Leucine
D.
Cysteine
E.
Histidine
Question #20
At pH = 0, the net charge on glutamic acid is:____________
A.
-1
B.
+1
C.
+2
D.
0
Question #21
At pH = 13, the net charge on lysine is:____________
A.
-1
B.
+2
C.
+1
D.
+3
Question #22
What is the charge of the dipeptide Ala-Lys a pH = 12?
A.
-1
B.
0
C.
+2
D.
+1
Question #23
The lowest charge possible for glutamic acid is
A.
-2
B.
-1
Question #24
The charge of cysteine at pH below 2 is
A.
+1
B.
-1
C.
-2
D.
0
Question #25
The charge of glutamic acid at pH > 10 is
A.
0
B.
+2
C.
+1
D.
-2
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