BIOC 384 PRACTICE TEST EXAM QUESTIONS AND
ANSWERS GRADED A+
✔✔What are the three-letter and one-letter abbreviations for the amino acid tyrosine?
Tyo, T
Tyr, R
Tro, Y
Tyr, Y - ✔✔Tyr, Y
✔✔Which linear sequence of bonded atoms can be found in the backbone of
polypeptides?
C-N-N-C
C-C-N-C
N-C-C-C
C-O-C-N - ✔✔C-C-N-C
✔✔The peptide bond
is most stable in the cis configuration.
has a mix of single and double bond characters.
can rotate around the carbonyl and N bond but not around the -carbon and N bond.
can function as a weak acid and weak base. - ✔✔has a mix of single and double bond
characters.
✔✔The peptide bond is stronger than the ester bond. What structural feature of the
peptide bond gives it additional bond strength?
Resonance structures give the peptide bond some double bond character.
The peptide bond is between carbon and nitrogen instead of carbon and oxygen atoms.
The peptide bond is more polar.
Peptide bonds can hydrogen bond. - ✔✔Resonance structures give the peptide bond
some double bond character.
✔✔All of the following are types of protein secondary structure EXCEPT
b-sheets.
b-helixes.
b-helixes.
b-turns. - ✔✔b-helixes.
✔✔Which statement regarding protein secondary structures is correct?
B-strands allow a-helices to interact with one another.
Protein a-helices alternate with a B-strands in stabilizing protein structure.
Protein a-helices are left handed, whereas B-sheets are right handed in arrangement.
Protein a-helices and B-strands differ in that a-helices are stabilized by intrahelical
hydrogen bonds, whereas B-strands are stabilized by hydrogen bonds across adjacent
,strands. - ✔✔Protein a-helices and B-strands differ in that a-helices are stabilized by
intrahelical hydrogen bonds, whereas B-strands are stabilized by hydrogen bonds
across adjacent strands.
✔✔What is the minimum number of amino acids needed to make one turn of an a-
helix?
3
4
6
7 - ✔✔4
✔✔Which of the following statements about B-sheet structures is true?
The individual strands of all B-sheet structures are connected by turns, helices, or
loops.
All amino acid side chains in antiparallel and parallel B-sheet structures point to one
side of the sheet.
Parallel -sheet structures have backbone amides that directly hydrogen bond between
strands, whereas antiparallel B-sheets have hydrogen bonds that are offset.
All B-sheet structures form a spiraling backbone chain. - ✔✔The individual strands of all
-sheet structures are connected by turns, helices, or loops.
✔✔What is a difference between parallel and antiparallel B-sheet secondary structures?
Antiparallel B-sheets have a larger number of stabilizing H bonds between backbone
amides than parallel B-sheets.
Parallel B-sheets require a larger loop connecting together the individual peptide
strands in the sheet.
Parallel B-sheets are longer than antiparallel sheets.
Parallel B-sheets have amino acid side chains alternating up and down, whereas
antiparallel side chains alternate down and up. - ✔✔Parallel B-sheets require a larger
loop connecting together the individual peptide strands in the sheet.
✔✔How many B-turns or B-loops are required to construct a B-sheet composed of four
antiparallel strands?
0
3
4
5 - ✔✔3
✔✔The protein fold known as the Rossman fold is found in proteins that commonly bind
a-helices.
nucleotides.
cytochromes.
membranes. - ✔✔nucleotides.
✔✔Protein tertiary structures
,require the formation of disulfide bonds in order to achieve their native state.
are always irreversibly destroyed by the addition of denaturants, such as urea and salts,
even when the denaturants are subsequently removed.
are often disrupted by the either very low pH or very high pH values as a result of
alterations in the ionization states of acidic or basic amino acids.
are generally poorly defined and cannot be determined experimentally. - ✔✔are often
disrupted by the either very low pH or very high pH values as a result of alterations in
the ionization states of acidic or basic amino acids
✔✔At the interface between subunits of a protein with quaternary structure, which of the
following interactions between amino acid side chains would contribute to the stability of
the dimer?
glutamate-aspartate.
leucine-aspartate.
glutamate-lysine.
phenylalaninelysine. - ✔✔glutamate-lysine.
✔✔In multi-subunit proteins, such as hemoglobin, the different subunits are usually
bound to one another by all of the following EXCEPT
hydrogen bonds.
electrostatic interactions.
hydrophobic interactions.
peptide bonds. - ✔✔peptide bonds.
✔✔Which gives rise to a favorable enthalpic (S) driving force for protein folding?
The lining up of hydrogen bonds as the protein folds.
The limiting of possible conformations as the protein folds.
The decrease in ordered water molecules as hydrophobic amino acids pack together.
The stabilization caused by favorable electrostatic interactions of amino acid side
chains. - ✔✔The decrease in ordered water molecules as hydrophobic amino acids
pack together.
✔✔Of the three proposed models of globular protein folding, which one describes the
initial formation of all secondary structures, followed by the arrangement of those
secondary structures into a final tertiary structure?
mutant globule
hydrophobic collapse model
framework model
nucleation model - ✔✔framework model
✔✔Why is the process of purifying proteins from cells considered challenging?
, Proteins are insoluble.
The process is expensive and time consuming.
There is no way to determine the structure of the protein.
There are 10,000 to 100,000 proteins in one sample. - ✔✔There are 10,000 to 100,000
proteins in one sample.
✔✔When preparing to isolate proteins from plant cells, the first step in preparing the cell
homogenate would be
sonication.
using a French press.
treatment with mild detergents.
enzymatic treatment. - ✔✔enzymatic treatment.
✔✔After centrifugation, the purity of the protein is determined by
absorbance measurements.
activity units.
total protein content.
specific activity. - ✔✔specific activity.
✔✔After centrifugation, there is a 10% decrease in activity and a 75% decrease in total
protein. What is purification of the target protein?
0.28-fold
1.3-fold
3.6-fold
7.5-fold - ✔✔3.6-fold
✔✔Calculate the specific activity when 500 mg of protein has an activity of 18,000 units.
0.28 units/mg protein
36 units/mg protein
9000 units/mg protein
13,000 units/mg protein - ✔✔9000 units/mg protein
✔✔The advantage of using a native PAGE gel compared with an SDS-PAGE gel is that
the native PAGE gel
separates proteins only based on molar mass.
gives information on the charge or conformation of the protein.
results in a better separation of small proteins.
increases the resolution of large and small proteins. - ✔✔gives information on the
charge or conformation of the protein.
ANSWERS GRADED A+
✔✔What are the three-letter and one-letter abbreviations for the amino acid tyrosine?
Tyo, T
Tyr, R
Tro, Y
Tyr, Y - ✔✔Tyr, Y
✔✔Which linear sequence of bonded atoms can be found in the backbone of
polypeptides?
C-N-N-C
C-C-N-C
N-C-C-C
C-O-C-N - ✔✔C-C-N-C
✔✔The peptide bond
is most stable in the cis configuration.
has a mix of single and double bond characters.
can rotate around the carbonyl and N bond but not around the -carbon and N bond.
can function as a weak acid and weak base. - ✔✔has a mix of single and double bond
characters.
✔✔The peptide bond is stronger than the ester bond. What structural feature of the
peptide bond gives it additional bond strength?
Resonance structures give the peptide bond some double bond character.
The peptide bond is between carbon and nitrogen instead of carbon and oxygen atoms.
The peptide bond is more polar.
Peptide bonds can hydrogen bond. - ✔✔Resonance structures give the peptide bond
some double bond character.
✔✔All of the following are types of protein secondary structure EXCEPT
b-sheets.
b-helixes.
b-helixes.
b-turns. - ✔✔b-helixes.
✔✔Which statement regarding protein secondary structures is correct?
B-strands allow a-helices to interact with one another.
Protein a-helices alternate with a B-strands in stabilizing protein structure.
Protein a-helices are left handed, whereas B-sheets are right handed in arrangement.
Protein a-helices and B-strands differ in that a-helices are stabilized by intrahelical
hydrogen bonds, whereas B-strands are stabilized by hydrogen bonds across adjacent
,strands. - ✔✔Protein a-helices and B-strands differ in that a-helices are stabilized by
intrahelical hydrogen bonds, whereas B-strands are stabilized by hydrogen bonds
across adjacent strands.
✔✔What is the minimum number of amino acids needed to make one turn of an a-
helix?
3
4
6
7 - ✔✔4
✔✔Which of the following statements about B-sheet structures is true?
The individual strands of all B-sheet structures are connected by turns, helices, or
loops.
All amino acid side chains in antiparallel and parallel B-sheet structures point to one
side of the sheet.
Parallel -sheet structures have backbone amides that directly hydrogen bond between
strands, whereas antiparallel B-sheets have hydrogen bonds that are offset.
All B-sheet structures form a spiraling backbone chain. - ✔✔The individual strands of all
-sheet structures are connected by turns, helices, or loops.
✔✔What is a difference between parallel and antiparallel B-sheet secondary structures?
Antiparallel B-sheets have a larger number of stabilizing H bonds between backbone
amides than parallel B-sheets.
Parallel B-sheets require a larger loop connecting together the individual peptide
strands in the sheet.
Parallel B-sheets are longer than antiparallel sheets.
Parallel B-sheets have amino acid side chains alternating up and down, whereas
antiparallel side chains alternate down and up. - ✔✔Parallel B-sheets require a larger
loop connecting together the individual peptide strands in the sheet.
✔✔How many B-turns or B-loops are required to construct a B-sheet composed of four
antiparallel strands?
0
3
4
5 - ✔✔3
✔✔The protein fold known as the Rossman fold is found in proteins that commonly bind
a-helices.
nucleotides.
cytochromes.
membranes. - ✔✔nucleotides.
✔✔Protein tertiary structures
,require the formation of disulfide bonds in order to achieve their native state.
are always irreversibly destroyed by the addition of denaturants, such as urea and salts,
even when the denaturants are subsequently removed.
are often disrupted by the either very low pH or very high pH values as a result of
alterations in the ionization states of acidic or basic amino acids.
are generally poorly defined and cannot be determined experimentally. - ✔✔are often
disrupted by the either very low pH or very high pH values as a result of alterations in
the ionization states of acidic or basic amino acids
✔✔At the interface between subunits of a protein with quaternary structure, which of the
following interactions between amino acid side chains would contribute to the stability of
the dimer?
glutamate-aspartate.
leucine-aspartate.
glutamate-lysine.
phenylalaninelysine. - ✔✔glutamate-lysine.
✔✔In multi-subunit proteins, such as hemoglobin, the different subunits are usually
bound to one another by all of the following EXCEPT
hydrogen bonds.
electrostatic interactions.
hydrophobic interactions.
peptide bonds. - ✔✔peptide bonds.
✔✔Which gives rise to a favorable enthalpic (S) driving force for protein folding?
The lining up of hydrogen bonds as the protein folds.
The limiting of possible conformations as the protein folds.
The decrease in ordered water molecules as hydrophobic amino acids pack together.
The stabilization caused by favorable electrostatic interactions of amino acid side
chains. - ✔✔The decrease in ordered water molecules as hydrophobic amino acids
pack together.
✔✔Of the three proposed models of globular protein folding, which one describes the
initial formation of all secondary structures, followed by the arrangement of those
secondary structures into a final tertiary structure?
mutant globule
hydrophobic collapse model
framework model
nucleation model - ✔✔framework model
✔✔Why is the process of purifying proteins from cells considered challenging?
, Proteins are insoluble.
The process is expensive and time consuming.
There is no way to determine the structure of the protein.
There are 10,000 to 100,000 proteins in one sample. - ✔✔There are 10,000 to 100,000
proteins in one sample.
✔✔When preparing to isolate proteins from plant cells, the first step in preparing the cell
homogenate would be
sonication.
using a French press.
treatment with mild detergents.
enzymatic treatment. - ✔✔enzymatic treatment.
✔✔After centrifugation, the purity of the protein is determined by
absorbance measurements.
activity units.
total protein content.
specific activity. - ✔✔specific activity.
✔✔After centrifugation, there is a 10% decrease in activity and a 75% decrease in total
protein. What is purification of the target protein?
0.28-fold
1.3-fold
3.6-fold
7.5-fold - ✔✔3.6-fold
✔✔Calculate the specific activity when 500 mg of protein has an activity of 18,000 units.
0.28 units/mg protein
36 units/mg protein
9000 units/mg protein
13,000 units/mg protein - ✔✔9000 units/mg protein
✔✔The advantage of using a native PAGE gel compared with an SDS-PAGE gel is that
the native PAGE gel
separates proteins only based on molar mass.
gives information on the charge or conformation of the protein.
results in a better separation of small proteins.
increases the resolution of large and small proteins. - ✔✔gives information on the
charge or conformation of the protein.
