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 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.
neutral molecule or an ion
C.
acid or a base
D.
transparent or a light-absorbing compound
E.
polar or a nonpolar molecule
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.
—COO– + —NH2+ → —COOH + —NH2
B.
—COOH + —NH2 → —COO– + —NH2+
C.
—NH2 + OH– → —NH– + H2O
D.
—NH3+ + OH– → —NH2 + H2O
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.
no net charge
C.
a net positive charge
D.
positive and negative charges in equal concentration
E.
a net negative charge
Question #5
The formation of a peptide bond between two amino acids is an example of a(n) ______________ reaction.
A.
group transfer
B.
oxidation reduction
C.
condensation
D.
cleavage
E.
isomerization
Question #6
At the isoelectric pH of a tetrapeptide:
A.
the amino and carboxyl termini are not charged
B.
only the amino and carboxyl termini contribute charge
C.
the total net charge is zero
D.
there are four ionic charges
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 fibrous region of a globular protein
C.
a subunit of an oligomeric protein
D.
synonymous with “protomer”
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.
Methionine
B.
Arginine
C.
Leucine
D.
Phenylalanine
E.
Glycine
Question #9
An essential amino acid is one that
A.
the body cannot synthesize
B.
is essentially easy to 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.
Aspartate & Glutamate
B.
Leucine & Glycine
C.
Histidine & Lysine
D.
Asparagine & Glutamine
Question #11
How many different standard amino acids are there?
A.
3
B.
20
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.
lysine; contains only nitrogen
B.
proline; forms a covalent bond with the amino group
C.
glycine; is unbranched
D.
glycine; is a hydrogen atom
E.
alanine; is a simple methyl group
Question #13
Which of the following is an amino acid?
A.
Glycine
B.
Alanine
C.
Proline
D.
Serine
Question #14
A protease
A.
is an enzyme that catalyzes proteolysis, the breakdown of proteins into smaller polypeptides or single amino acids
B.
All the above statements are correct
C.
cleaves proteins by the addition of a molecule of water to a peptide bond
D.
is also called a peptidase or proteinase
E.
increases the rate of proteolysis
Question #15
Proteases
A.
three of the choices are correct
B.
Produce amino acids or short peptides
C.
cleaves disulfide bonds
D.
Degrade proteins
E.
Cleave peptide bonds
Question #16
Chose the best true statement
A.
Two of the statement are incorrect
B.
Cleave all peptide bonds
C.
Proteases are involved in anabolism
D.
Proteases are involved in many biological functions, including digestion of eaten proteins, and protein catabolism
E.
Proteases can cleave at specific points in the peptide chain
Question #17
The fully protonated form of histidine has a ____________charge.
A.
+1
B.
+3
C.
+2
D.
+4
Question #18
Which of the following amino acids has a net negative charge at physiologic pH (~7.4)?
A.
Lysine
B.
Histidine
C.
Glutamic Acid
D.
Asparagine
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.
Glutamic acid
D.
Tyrosine
E.
Cysteine
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.
+3
B.
+2
C.
+1
D.
-1
Question #22
What is the charge of the dipeptide Ala-Lys a pH = 12?
A.
-1
B.
+2
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.
-1
B.
+1
C.
0
D.
-2
Question #25
The charge of glutamic acid at pH > 10 is
A.
0
B.
+2
C.
+1
D.
-2
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