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.
is a carboxylic acid
C.
is symmetric
D.
is in the L absolute configuration in naturally occurring proteins
E.
has no net charge
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 + OH– → —COO– + H2O
C.
—NH2 + OH– → —NH– + H2O
D.
—NH3+ + OH– → —NH2 + H2O
E.
—COOH + —NH2 → —COO– + —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.
no charged groups
C.
positive and negative charges in equal concentration
D.
a net negative charge
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.
oxidation reduction
B.
group transfer
C.
cleavage
D.
condensation
E.
isomerization
Question #6
At the isoelectric pH of a tetrapeptide:
A.
the total net charge is zero
B.
there are four ionic charges
C.
the amino and carboxyl termini are not charged
D.
two internal amino acids of the tetrapeptide cannot have ionizable R groups
E.
only the amino and carboxyl termini contribute charge
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 fibrous region of a globular protein
D.
synonymous with “protomer”
E.
a part of the protein that is not composed of amino acids
Question #8
Which one of the following amino acids contains an aromatic group?
A.
Arginine
B.
Glycine
C.
Phenylalanine
D.
Methionine
E.
Leucine
Question #9
An essential amino acid is one that
A.
is essentially easy to synthesize
B.
is essential to flagella motion
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.
Histidine & Lysine
C.
Asparagine & Glutamine
D.
Leucine & Glycine
Question #11
How many different standard amino acids are there?
A.
20
B.
100
C.
an infinite number
D.
3
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.
proline; forms a covalent bond with the amino group
C.
lysine; contains only nitrogen
D.
glycine; is unbranched
E.
glycine; is a hydrogen atom
Question #13
Which of the following is an amino acid?
A.
Glycine
B.
Serine
C.
Alanine
D.
Proline
Question #14
A protease
A.
cleaves proteins by the addition of a molecule of water to a peptide bond
B.
All the above statements are correct
C.
is also called a peptidase or proteinase
D.
increases the rate of proteolysis
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.
three of the choices are correct
C.
cleaves disulfide bonds
D.
Cleave peptide bonds
E.
Degrade proteins
Question #16
Chose the best true statement
A.
Proteases can cleave at specific points in the peptide chain
B.
Two of the statement are incorrect
C.
Proteases are involved in anabolism
D.
Proteases are involved in many biological functions, including digestion of eaten proteins, and protein catabolism
E.
Cleave all peptide bonds
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.
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.
Histidine
B.
Tyrosine
C.
Leucine
D.
Glutamic acid
E.
Cysteine
Question #20
At pH = 0, the net charge on glutamic acid is:____________
A.
-1
B.
+1
C.
+2
D.
0
Question #21
At pH = 13, the net charge on lysine is:____________
A.
-1
B.
+3
C.
+2
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.
0
B.
-1
C.
-2
D.
+1
Question #25
The charge of glutamic acid at pH > 10 is
A.
+2
B.
+1
C.
-2
D.
0
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