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 a carboxylic acid
C.
is symmetric
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.
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.
—NH2 + OH– → —NH– + H2O
B.
—COOH + OH– → —COO– + H2O
C.
—COO– + —NH2+ → —COOH + —NH2
D.
—COOH + —NH2 → —COO– + —NH2+
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.
a net negative charge
C.
positive and negative charges in equal concentration
D.
no charged groups
E.
no net 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.
group transfer
D.
cleavage
E.
condensation
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.
synonymous with “protomer”
C.
a part of the protein that is not composed of amino acids
D.
a fibrous region of a globular protein
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.
is essential to flagella motion
B.
is essentially easy to synthesize
C.
the body can synthesize under essential conditions
D.
the body cannot 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.
Aspartate & Glutamate
B.
Asparagine & Glutamine
C.
Leucine & Glycine
D.
Histidine & Lysine
Question #11
How many different standard amino acids are there?
A.
100
B.
3
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.
glycine; is a hydrogen atom
B.
glycine; is unbranched
C.
proline; forms a covalent bond with the amino group
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.
Glycine
C.
Proline
D.
Serine
Question #14
A protease
A.
is also called a peptidase or proteinase
B.
increases the rate of proteolysis
C.
is an enzyme that catalyzes proteolysis, the breakdown of proteins into smaller polypeptides or single amino acids
D.
All the above statements are correct
E.
cleaves proteins by the addition of a molecule of water to a peptide bond
Question #15
Proteases
A.
Cleave peptide bonds
B.
cleaves disulfide bonds
C.
Degrade proteins
D.
Produce amino acids or short peptides
E.
three of the choices are correct
Question #16
Chose the best true statement
A.
Proteases are involved in anabolism
B.
Two of the statement are incorrect
C.
Cleave all peptide bonds
D.
Proteases can cleave at specific points in the peptide chain
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.
+3
B.
+2
C.
+4
D.
+1
Question #18
Which of the following amino acids has a net negative charge at physiologic pH (~7.4)?
A.
Asparagine
B.
Glutamic Acid
C.
Lysine
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.
Histidine
C.
Glutamic acid
D.
Leucine
E.
Tyrosine
Question #20
At pH = 0, the net charge on glutamic acid is:____________
A.
+1
B.
+2
C.
-1
D.
0
Question #21
At pH = 13, the net charge on lysine is:____________
A.
+1
B.
+2
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.
-1
C.
0
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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