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 bonded to four different chemical groups
C.
is symmetric
D.
is in the L absolute configuration in naturally occurring proteins
E.
is a carboxylic acid
Question #2
Amino acids are ampholytes because they can function as either a(n):
A.
standard or a nonstandard monomer in proteins
B.
transparent or a light-absorbing compound
C.
polar or a nonpolar molecule
D.
neutral molecule or an ion
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.
—NH2 + OH– → —NH– + H2O
B.
—NH3+ + OH– → —NH2 + H2O
C.
—COOH + —NH2 → —COO– + —NH2+
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 charged groups
B.
a net positive charge
C.
positive and negative charges in equal concentration
D.
a net negative charge
E.
no net charge
Question #5
The formation of a peptide bond between two amino acids is an example of a(n) ______________ reaction.
A.
condensation
B.
group transfer
C.
isomerization
D.
oxidation reduction
E.
cleavage
Question #6
At the isoelectric pH of a tetrapeptide:
A.
there are four ionic charges
B.
two internal amino acids of the tetrapeptide cannot have ionizable R groups
C.
only the amino and carboxyl termini contribute charge
D.
the total net charge is zero
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.
a part of the protein that is not composed of amino acids
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.
Leucine
B.
Phenylalanine
C.
Arginine
D.
Methionine
E.
Glycine
Question #9
An essential amino acid is one that
A.
the body cannot synthesize
B.
is essential to flagella motion
C.
is essentially easy to synthesize
D.
the body can synthesize under essential conditions
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.
Leucine & Glycine
D.
Histidine & Lysine
Question #11
How many different standard amino acids are there?
A.
3
B.
100
C.
an infinite number
D.
20
Question #12
Of the 20 standard amino acids, only ___________ is not optically active (nonchiral). The reason is that its side chain ___________.
A.
lysine; contains only nitrogen
B.
glycine; is a hydrogen atom
C.
glycine; is unbranched
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.
Proline
D.
Alanine
Question #14
A protease
A.
increases the rate of proteolysis
B.
is an enzyme that catalyzes proteolysis, the breakdown of proteins into smaller polypeptides or single amino acids
C.
cleaves proteins by the addition of a molecule of water to a peptide bond
D.
is also called a peptidase or proteinase
E.
All the above statements are correct
Question #15
Proteases
A.
Cleave peptide bonds
B.
cleaves disulfide bonds
C.
Produce amino acids or short peptides
D.
Degrade proteins
E.
three of the choices are correct
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.
Cleave all peptide bonds
D.
Proteases are involved in anabolism
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.
+1
B.
+4
C.
+2
D.
+3
Question #18
Which of the following amino acids has a net negative charge at physiologic pH (~7.4)?
A.
Glutamic Acid
B.
Histidine
C.
Asparagine
D.
Lysine
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.
Histidine
C.
Tyrosine
D.
Glutamic acid
E.
Cysteine
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.
+3
B.
+2
C.
-1
D.
+1
Question #22
What is the charge of the dipeptide Ala-Lys a pH = 12?
A.
+2
B.
+1
C.
0
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.
0
B.
-2
C.
+1
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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