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 symmetric
C.
is bonded to four different chemical groups
D.
is a carboxylic acid
E.
has no net charge
Question #2
Amino acids are ampholytes because they can function as either a(n):
A.
neutral molecule or an ion
B.
acid or a base
C.
transparent or a light-absorbing compound
D.
polar or a nonpolar molecule
E.
standard or a nonstandard monomer in proteins
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 + OH– → —COO– + H2O
B.
—NH2 + OH– → —NH– + H2O
C.
—NH3+ + OH– → —NH2 + H2O
D.
—COOH + —NH2 → —COO– + —NH2+
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 net charge
B.
no charged groups
C.
a net negative charge
D.
a net positive charge
E.
positive and negative charges in equal concentration
Question #5
The formation of a peptide bond between two amino acids is an example of a(n) ______________ reaction.
A.
group transfer
B.
condensation
C.
oxidation reduction
D.
cleavage
E.
isomerization
Question #6
At the isoelectric pH of a tetrapeptide:
A.
two internal amino acids of the tetrapeptide cannot have ionizable R groups
B.
there are four ionic charges
C.
the total net charge is zero
D.
the amino and carboxyl termini are not charged
E.
only the amino and carboxyl termini contribute charge
Question #7
A prosthetic group is:
A.
synonymous with “protomer”
B.
a fibrous region of a globular protein
C.
a nonidentical subunit of a protein with many identical subunits
D.
a part of the protein that is not composed of amino acids
E.
a subunit of an oligomeric protein
Question #8
Which one of the following amino acids contains an aromatic group?
A.
Methionine
B.
Phenylalanine
C.
Leucine
D.
Arginine
E.
Glycine
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.
Leucine & Glycine
C.
Histidine & Lysine
D.
Asparagine & Glutamine
Question #11
How many different standard amino acids are there?
A.
3
B.
20
C.
100
D.
an infinite number
Question #12
Of the 20 standard amino acids, only ___________ is not optically active (nonchiral). The reason is that its side chain ___________.
A.
glycine; is unbranched
B.
proline; forms a covalent bond with the amino group
C.
glycine; is a hydrogen atom
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.
Proline
C.
Serine
D.
Glycine
Question #14
A protease
A.
is an enzyme that catalyzes proteolysis, the breakdown of proteins into smaller polypeptides or single amino acids
B.
cleaves proteins by the addition of a molecule of water to a peptide bond
C.
is also called a peptidase or proteinase
D.
All the above statements are correct
E.
increases the rate of proteolysis
Question #15
Proteases
A.
Degrade proteins
B.
three of the choices are correct
C.
Cleave peptide bonds
D.
Produce amino acids or short peptides
E.
cleaves disulfide bonds
Question #16
Chose the best true statement
A.
Proteases are involved in anabolism
B.
Cleave all peptide bonds
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.
Two of the statement are incorrect
Question #17
The fully protonated form of histidine has a ____________charge.
A.
+1
B.
+2
C.
+3
D.
+4
Question #18
Which of the following amino acids has a net negative charge at physiologic pH (~7.4)?
A.
Lysine
B.
Glutamic Acid
C.
Histidine
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.
Glutamic acid
C.
Tyrosine
D.
Cysteine
E.
Histidine
Question #20
At pH = 0, the net charge on glutamic acid is:____________
A.
+2
B.
+1
C.
0
D.
-1
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.
+2
C.
0
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.
-2
C.
-1
D.
0
Question #25
The charge of glutamic acid at pH > 10 is
A.
+2
B.
-2
C.
+1
D.
0
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