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.
has no net charge
C.
is a carboxylic acid
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.
neutral molecule or an ion
B.
polar or a nonpolar molecule
C.
standard or a nonstandard monomer in proteins
D.
transparent or a light-absorbing compound
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.
—COO– + —NH2+ → —COOH + —NH2
B.
—COOH + —NH2 → —COO– + —NH2+
C.
—NH3+ + OH– → —NH2 + H2O
D.
—NH2 + OH– → —NH– + H2O
E.
—COOH + OH– → —COO– + 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.
a net negative charge
B.
no charged groups
C.
a net positive charge
D.
no net charge
E.
positive and negative charges in equal concentration
Question #5
The formation of a peptide bond between two amino acids is an example of a(n) ______________ reaction.
A.
condensation
B.
isomerization
C.
cleavage
D.
oxidation reduction
E.
group transfer
Question #6
At the isoelectric pH of a tetrapeptide:
A.
there are four ionic charges
B.
the amino and carboxyl termini are not charged
C.
the total net charge is zero
D.
only the amino and carboxyl termini contribute charge
E.
two internal amino acids of the tetrapeptide cannot have ionizable R groups
Question #7
A prosthetic group is:
A.
a subunit of an oligomeric protein
B.
a fibrous region of a globular protein
C.
a part of the protein that is not composed of amino acids
D.
synonymous with “protomer”
E.
a nonidentical subunit of a protein with many identical subunits
Question #8
Which one of the following amino acids contains an aromatic group?
A.
Leucine
B.
Arginine
C.
Glycine
D.
Methionine
E.
Phenylalanine
Question #9
An essential amino acid is one that
A.
the body cannot synthesize
B.
is essential to flagella motion
C.
the body can synthesize under essential conditions
D.
is essentially easy to synthesize
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.
Aspartate & Glutamate
D.
Histidine & Lysine
Question #11
How many different standard amino acids are there?
A.
20
B.
100
C.
3
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.
lysine; contains only nitrogen
C.
proline; forms a covalent bond with the amino group
D.
glycine; is a hydrogen atom
E.
glycine; is unbranched
Question #13
Which of the following is an amino acid?
A.
Alanine
B.
Glycine
C.
Proline
D.
Serine
Question #14
A protease
A.
cleaves proteins by the addition of a molecule of water to a peptide bond
B.
increases the rate of proteolysis
C.
All the above statements are correct
D.
is an enzyme that catalyzes proteolysis, the breakdown of proteins into smaller polypeptides or single amino acids
E.
is also called a peptidase or proteinase
Question #15
Proteases
A.
Degrade proteins
B.
Produce amino acids or short peptides
C.
cleaves disulfide bonds
D.
Cleave peptide bonds
E.
three of the choices are correct
Question #16
Chose the best true statement
A.
Proteases are involved in many biological functions, including digestion of eaten proteins, and protein catabolism
B.
Proteases can cleave at specific points in the peptide chain
C.
Two of the statement are incorrect
D.
Proteases are involved in anabolism
E.
Cleave all peptide bonds
Question #17
The fully protonated form of histidine has a ____________charge.
A.
+1
B.
+2
C.
+4
D.
+3
Question #18
Which of the following amino acids has a net negative charge at physiologic pH (~7.4)?
A.
Lysine
B.
Asparagine
C.
Glutamic Acid
D.
Histidine
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.
Cysteine
B.
Tyrosine
C.
Histidine
D.
Glutamic acid
E.
Leucine
Question #20
At pH = 0, the net charge on glutamic acid is:____________
A.
+2
B.
0
C.
-1
D.
+1
Question #21
At pH = 13, the net charge on lysine is:____________
A.
+3
B.
+2
C.
-1
D.
+1
Question #22
What is the charge of the dipeptide Ala-Lys a pH = 12?
A.
+2
B.
0
C.
-1
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.
-2
B.
0
C.
-1
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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