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 bonded to four different chemical groups
B.
is symmetric
C.
is in the L absolute configuration in naturally occurring proteins
D.
has no net charge
E.
is a carboxylic acid
Question #2
Amino acids are ampholytes because they can function as either a(n):
A.
acid or a base
B.
neutral molecule or an ion
C.
polar or a nonpolar molecule
D.
transparent or a light-absorbing compound
E.
standard or a nonstandard monomer in proteins
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 + —NH2 → —COO– + —NH2+
B.
—NH2 + OH– → —NH– + H2O
C.
—COO– + —NH2+ → —COOH + —NH2
D.
—COOH + OH– → —COO– + H2O
E.
—NH3+ + OH– → —NH2 + 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 positive charge
B.
no charged groups
C.
no net charge
D.
a net negative 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.
oxidation reduction
B.
isomerization
C.
group transfer
D.
condensation
E.
cleavage
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 part of the protein that is not composed of amino acids
B.
a nonidentical subunit of a protein with many identical subunits
C.
a subunit of an oligomeric protein
D.
a fibrous region of a globular protein
E.
synonymous with “protomer”
Question #8
Which one of the following amino acids contains an aromatic group?
A.
Glycine
B.
Arginine
C.
Phenylalanine
D.
Leucine
E.
Methionine
Question #9
An essential amino acid is one that
A.
the body cannot synthesize
B.
the body can synthesize under essential conditions
C.
is essentially easy to 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.
Histidine & Lysine
B.
Aspartate & Glutamate
C.
Asparagine & Glutamine
D.
Leucine & Glycine
Question #11
How many different standard amino acids are there?
A.
20
B.
3
C.
an infinite number
D.
100
Question #12
Of the 20 standard amino acids, only ___________ is not optically active (nonchiral). The reason is that its side chain ___________.
A.
glycine; is unbranched
B.
proline; forms a covalent bond with the amino group
C.
glycine; is a hydrogen atom
D.
alanine; is a simple methyl group
E.
lysine; contains only nitrogen
Question #13
Which of the following is an amino acid?
A.
Alanine
B.
Proline
C.
Serine
D.
Glycine
Question #14
A protease
A.
is also called a peptidase or proteinase
B.
cleaves proteins by the addition of a molecule of water to a peptide bond
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.
increases the rate of proteolysis
Question #15
Proteases
A.
Cleave peptide bonds
B.
cleaves disulfide bonds
C.
Degrade proteins
D.
three of the choices are correct
E.
Produce amino acids or short peptides
Question #16
Chose the best true statement
A.
Two of the statement are incorrect
B.
Proteases can cleave at specific points in the peptide chain
C.
Proteases are involved in anabolism
D.
Cleave all peptide bonds
E.
Proteases are involved in many biological functions, including digestion of eaten proteins, and protein catabolism
Question #17
The fully protonated form of histidine has a ____________charge.
A.
+4
B.
+1
C.
+3
D.
+2
Question #18
Which of the following amino acids has a net negative charge at physiologic pH (~7.4)?
A.
Glutamic Acid
B.
Lysine
C.
Asparagine
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.
Leucine
B.
Cysteine
C.
Histidine
D.
Glutamic acid
E.
Tyrosine
Question #20
At pH = 0, the net charge on glutamic acid is:____________
A.
0
B.
+2
C.
+1
D.
-1
Question #21
At pH = 13, the net charge on lysine is:____________
A.
+2
B.
+1
C.
+3
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.
+1
B.
-2
C.
0
D.
-1
Question #25
The charge of glutamic acid at pH > 10 is
A.
+1
B.
0
C.
+2
D.
-2
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