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 in the L absolute configuration in naturally occurring proteins
B.
is a carboxylic acid
C.
has no net charge
D.
is symmetric
E.
is bonded to four different chemical groups
Question #2
Amino acids are ampholytes because they can function as either a(n):
A.
neutral molecule or an ion
B.
standard or a nonstandard monomer in proteins
C.
transparent or a light-absorbing compound
D.
polar or a nonpolar molecule
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.
—COOH + —NH2 → —COO– + —NH2+
B.
—NH2 + OH– → —NH– + H2O
C.
—NH3+ + OH– → —NH2 + H2O
D.
—COO– + —NH2+ → —COOH + —NH2
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 net charge
B.
positive and negative charges in equal concentration
C.
a net negative charge
D.
a net positive charge
E.
no charged groups
Question #5
The formation of a peptide bond between two amino acids is an example of a(n) ______________ reaction.
A.
condensation
B.
isomerization
C.
group transfer
D.
cleavage
E.
oxidation reduction
Question #6
At the isoelectric pH of a tetrapeptide:
A.
the total net charge is zero
B.
only the amino and carboxyl termini contribute charge
C.
the amino and carboxyl termini are not charged
D.
two internal amino acids of the tetrapeptide cannot have ionizable R groups
E.
there are four ionic charges
Question #7
A prosthetic group is:
A.
synonymous with “protomer”
B.
a nonidentical subunit of a protein with many identical subunits
C.
a subunit of an oligomeric protein
D.
a fibrous region of a globular protein
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.
Leucine
B.
Glycine
C.
Phenylalanine
D.
Methionine
E.
Arginine
Question #9
An essential amino acid is one that
A.
is essentially easy to synthesize
B.
the body can synthesize under essential conditions
C.
the body cannot synthesize
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.
Histidine & Lysine
C.
Leucine & Glycine
D.
Aspartate & Glutamate
Question #11
How many different standard amino acids are there?
A.
an infinite number
B.
3
C.
20
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.
glycine; is unbranched
C.
alanine; is a simple methyl group
D.
glycine; is a hydrogen atom
E.
proline; forms a covalent bond with the amino group
Question #13
Which of the following is an amino acid?
A.
Serine
B.
Glycine
C.
Alanine
D.
Proline
Question #14
A protease
A.
All the above statements are correct
B.
is also called a peptidase or proteinase
C.
increases the rate of proteolysis
D.
cleaves proteins by the addition of a molecule of water to a peptide bond
E.
is an enzyme that catalyzes proteolysis, the breakdown of proteins into smaller polypeptides or single amino acids
Question #15
Proteases
A.
Cleave peptide bonds
B.
Degrade proteins
C.
three of the choices are correct
D.
Produce amino acids or short peptides
E.
cleaves disulfide bonds
Question #16
Chose the best true statement
A.
Two of the statement are incorrect
B.
Proteases are involved in anabolism
C.
Proteases are involved in many biological functions, including digestion of eaten proteins, and protein catabolism
D.
Proteases can cleave at specific points in the peptide chain
E.
Cleave all peptide bonds
Question #17
The fully protonated form of histidine has a ____________charge.
A.
+1
B.
+3
C.
+4
D.
+2
Question #18
Which of the following amino acids has a net negative charge at physiologic pH (~7.4)?
A.
Glutamic Acid
B.
Asparagine
C.
Histidine
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.
Cysteine
B.
Leucine
C.
Histidine
D.
Glutamic acid
E.
Tyrosine
Question #20
At pH = 0, the net charge on glutamic acid is:____________
A.
-1
B.
0
C.
+1
D.
+2
Question #21
At pH = 13, the net charge on lysine is:____________
A.
+2
B.
-1
C.
+1
D.
+3
Question #22
What is the charge of the dipeptide Ala-Lys a pH = 12?
A.
+2
B.
0
C.
+1
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.
-2
B.
+1
C.
0
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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