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 in the L absolute configuration in naturally occurring proteins
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.
polar or a nonpolar molecule
B.
acid or a base
C.
standard or a nonstandard monomer in proteins
D.
transparent or a light-absorbing compound
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.
—NH3+ + OH– → —NH2 + H2O
B.
—NH2 + OH– → —NH– + H2O
C.
—COOH + —NH2 → —COO– + —NH2+
D.
—COO– + —NH2+ → —COOH + —NH2
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.
no charged groups
B.
a net negative charge
C.
no net 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.
isomerization
B.
oxidation reduction
C.
cleavage
D.
condensation
E.
group transfer
Question #6
At the isoelectric pH of a tetrapeptide:
A.
only the amino and carboxyl termini contribute charge
B.
the total net charge is zero
C.
two internal amino acids of the tetrapeptide cannot have ionizable R groups
D.
there are four ionic charges
E.
the amino and carboxyl termini are not charged
Question #7
A prosthetic group is:
A.
a subunit of an oligomeric protein
B.
a nonidentical subunit of a protein with many identical subunits
C.
synonymous with “protomer”
D.
a part of the protein that is not composed of amino acids
E.
a fibrous region of a globular protein
Question #8
Which one of the following amino acids contains an aromatic group?
A.
Phenylalanine
B.
Leucine
C.
Arginine
D.
Glycine
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.
Leucine & Glycine
B.
Histidine & Lysine
C.
Aspartate & Glutamate
D.
Asparagine & Glutamine
Question #11
How many different standard amino acids are there?
A.
3
B.
20
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 unbranched
B.
glycine; is a hydrogen atom
C.
alanine; is a simple methyl group
D.
lysine; contains only nitrogen
E.
proline; forms a covalent bond with the amino group
Question #13
Which of the following is an amino acid?
A.
Serine
B.
Proline
C.
Glycine
D.
Alanine
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.
is also called a peptidase or proteinase
D.
All the above statements are correct
E.
is an enzyme that catalyzes proteolysis, the breakdown of proteins into smaller polypeptides or single amino acids
Question #15
Proteases
A.
cleaves disulfide bonds
B.
Degrade proteins
C.
Produce amino acids or short peptides
D.
three of the choices are correct
E.
Cleave peptide bonds
Question #16
Chose the best true statement
A.
Proteases are involved in anabolism
B.
Proteases are involved in many biological functions, including digestion of eaten proteins, and protein catabolism
C.
Cleave all peptide bonds
D.
Proteases can cleave at specific points in the peptide chain
E.
Two of the statement are incorrect
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.
Glutamic acid
B.
Tyrosine
C.
Cysteine
D.
Leucine
E.
Histidine
Question #20
At pH = 0, the net charge on glutamic acid is:____________
A.
-1
B.
0
C.
+1
D.
+2
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.
+1
B.
0
C.
+2
D.
-1
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.
+1
B.
0
C.
-1
D.
-2
Question #25
The charge of glutamic acid at pH > 10 is
A.
-2
B.
+1
C.
+2
D.
0
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