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.
has no net charge
C.
is symmetric
D.
is a carboxylic acid
E.
is in the L absolute configuration in naturally occurring proteins
Question #2
Amino acids are ampholytes because they can function as either a(n):
A.
polar or a nonpolar molecule
B.
transparent or a light-absorbing compound
C.
neutral molecule or an ion
D.
standard or a nonstandard monomer in proteins
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.
—NH3+ + OH– → —NH2 + H2O
B.
—COOH + —NH2 → —COO– + —NH2+
C.
—NH2 + OH– → —NH– + H2O
D.
—COOH + OH– → —COO– + H2O
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 net charge
B.
a net negative charge
C.
positive and negative charges in equal concentration
D.
no charged groups
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.
cleavage
C.
condensation
D.
group transfer
E.
oxidation reduction
Question #6
At the isoelectric pH of a tetrapeptide:
A.
the amino and carboxyl termini are not charged
B.
the total net charge is zero
C.
two internal amino acids of the tetrapeptide cannot have ionizable R groups
D.
only the amino and carboxyl termini contribute charge
E.
there are four ionic charges
Question #7
A prosthetic group is:
A.
a fibrous region of a globular 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 subunit of an oligomeric protein
Question #8
Which one of the following amino acids contains an aromatic group?
A.
Arginine
B.
Glycine
C.
Leucine
D.
Phenylalanine
E.
Methionine
Question #9
An essential amino acid is one that
A.
is essentially easy to synthesize
B.
the body cannot synthesize
C.
the body can synthesize under essential conditions
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.
Asparagine & Glutamine
B.
Aspartate & Glutamate
C.
Histidine & Lysine
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.
alanine; is a simple methyl group
B.
lysine; contains only nitrogen
C.
glycine; is a hydrogen atom
D.
proline; forms a covalent bond with the amino group
E.
glycine; is unbranched
Question #13
Which of the following is an amino acid?
A.
Alanine
B.
Proline
C.
Glycine
D.
Serine
Question #14
A protease
A.
All the above statements are correct
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.
is an enzyme that catalyzes proteolysis, the breakdown of proteins into smaller polypeptides or single amino acids
Question #15
Proteases
A.
Produce amino acids or short peptides
B.
Cleave peptide bonds
C.
three of the choices are correct
D.
Degrade proteins
E.
cleaves disulfide bonds
Question #16
Chose the best true statement
A.
Proteases can cleave at specific points in the peptide chain
B.
Cleave all peptide bonds
C.
Proteases are involved in many biological functions, including digestion of eaten proteins, and protein catabolism
D.
Two of the statement are incorrect
E.
Proteases are involved in anabolism
Question #17
The fully protonated form of histidine has a ____________charge.
A.
+4
B.
+2
C.
+1
D.
+3
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.
Leucine
B.
Glutamic acid
C.
Histidine
D.
Cysteine
E.
Tyrosine
Question #20
At pH = 0, the net charge on glutamic acid is:____________
A.
0
B.
-1
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.
0
B.
-1
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.
0
C.
+2
D.
+1
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