QBM EXAM 2 QUESTIONS AND ANSWERS
Which of the following CANNOT be used to produce a 500 amino acid protein?
A) In vitro systems.
B) E. coli.
C) insect cells.
D) Plant cells.
E) Organic synthesis. - CORRECT ANSWER✅✅E) Organic synthesis.
Why are certain lines of E. coli (like BL21) used for protein expression?
A) They express lon and ompT proteases.
B) They contain the β-galactosidase gene on their genome.
C) They contain an ampicillin resistance gene on their genome.
D) They contain the T7 RNA polymerase gene on their genome.
E) They can outcompete wild-type E. coli. - CORRECT ANSWER✅✅D) They contain the T7 RNA
polymerase gene on their genome.
In the Ptac expression system,
A) the lac repressor protein is bound to the T7 promoter.
B) E. coli RNA polymerase transcribes the gene of interest into mRNA.
C) T7 RNA polymerase is bound to the T7 promoter.
D) the lac repressor protein is bound upstream of the T7 RNA polymerase gene.
E) IPTG is bound to the promoter. - CORRECT ANSWER✅✅B) E. coli RNA polymerase transcribes the
gene of interest into mRNA.
In the Ptac expression vector system, ___ is added to the media to induce protein expression by
inactivating the ______, allowing RNA polymerase to transcribe the gene of interest.
A) IPTG ; lac repressor
B) IPTG ; promoter sequence
C) urea ; lac repressor
,D) urea ; promoter sequence
E) glycerol ; lac repressor - CORRECT ANSWER✅✅A) IPTG ; lac repressor
Which of the following CANNOT be used to lyse cells to yield stable protein?
A) Detergents
B) Enzymes
C) Pressure
D) Sonication
E) Heat - CORRECT ANSWER✅✅E) Heat
Which of the following can be used to refold inclusion bodies?
A) Guanidine-HCl.
B) Urea.
C) Chaotropic salts.
D) All of the answer choices are correct - CORRECT ANSWER✅✅D) All of the answer choices are correct
You express a his-tagged protein in E. coli, lyse the cells, spin them down, and perform a western blot
using an anti-his antibody. After seeing the results of the western blot below, you decide that your next
step should be to
A) purify the protein with metal chelate chromatography.
B) refold the insoluble fraction using guanidine.
C) give up on using E. coli since the protein was not expressed, and instead switch to a yeast-
based expression system.
D) purify the protein with immunoprecipitation using the anti-his antibody and agarose capture
beads.
E) re-express the cells at 42 °C overnight. - CORRECT ANSWER✅✅B) refold the insoluble fraction using
guanidine.
, You wish to use dialysis to determine if a 30 kDa and 40 kDa protein interact. You should mix both
proteins and place them into dialysis tubing with a ________ kDa cutoff, and test to see if a dimer
remains inside the tubing.
A) 25
B) 30
C) 35
D) 50
E) 75 - CORRECT ANSWER✅✅D) 50
You place a 20 kDa protein and a 50 kDa protein in a dialysis tubing that has a 30 kDa cutoff, and place it
in a beaker with buffer. If these proteins do not interact,
A) both proteins will remain inside of the dialysis tube.
B) the 50 kDa protein will equilibrate with the buffer.
C) the 20 kDa protein will equilibrate with the buffer.
D) both proteins will equilibrate with the buffer. - CORRECT ANSWER✅✅C) the 20 kDa protein will
equilibrate with the buffer.
What is the purpose of adding sodium azide (NaN3) to a protein sample?
A) To act as a cryoprotectant.
B) To reduce carboxyl groups.
C) To prevent microorganism growth.
D) To inhibit proteases.
E) To act as a buffer against changes in pH that fall outside of the range of Tris. - CORRECT
ANSWER✅✅C) To prevent microorganism growth.
Which of the following can be used as a protease inhibitor to prevent protein degradation?
A) Chaotropic salts.
B) EDTA.
C) Propylene glycol.
D) Ammonium sulfate.
Which of the following CANNOT be used to produce a 500 amino acid protein?
A) In vitro systems.
B) E. coli.
C) insect cells.
D) Plant cells.
E) Organic synthesis. - CORRECT ANSWER✅✅E) Organic synthesis.
Why are certain lines of E. coli (like BL21) used for protein expression?
A) They express lon and ompT proteases.
B) They contain the β-galactosidase gene on their genome.
C) They contain an ampicillin resistance gene on their genome.
D) They contain the T7 RNA polymerase gene on their genome.
E) They can outcompete wild-type E. coli. - CORRECT ANSWER✅✅D) They contain the T7 RNA
polymerase gene on their genome.
In the Ptac expression system,
A) the lac repressor protein is bound to the T7 promoter.
B) E. coli RNA polymerase transcribes the gene of interest into mRNA.
C) T7 RNA polymerase is bound to the T7 promoter.
D) the lac repressor protein is bound upstream of the T7 RNA polymerase gene.
E) IPTG is bound to the promoter. - CORRECT ANSWER✅✅B) E. coli RNA polymerase transcribes the
gene of interest into mRNA.
In the Ptac expression vector system, ___ is added to the media to induce protein expression by
inactivating the ______, allowing RNA polymerase to transcribe the gene of interest.
A) IPTG ; lac repressor
B) IPTG ; promoter sequence
C) urea ; lac repressor
,D) urea ; promoter sequence
E) glycerol ; lac repressor - CORRECT ANSWER✅✅A) IPTG ; lac repressor
Which of the following CANNOT be used to lyse cells to yield stable protein?
A) Detergents
B) Enzymes
C) Pressure
D) Sonication
E) Heat - CORRECT ANSWER✅✅E) Heat
Which of the following can be used to refold inclusion bodies?
A) Guanidine-HCl.
B) Urea.
C) Chaotropic salts.
D) All of the answer choices are correct - CORRECT ANSWER✅✅D) All of the answer choices are correct
You express a his-tagged protein in E. coli, lyse the cells, spin them down, and perform a western blot
using an anti-his antibody. After seeing the results of the western blot below, you decide that your next
step should be to
A) purify the protein with metal chelate chromatography.
B) refold the insoluble fraction using guanidine.
C) give up on using E. coli since the protein was not expressed, and instead switch to a yeast-
based expression system.
D) purify the protein with immunoprecipitation using the anti-his antibody and agarose capture
beads.
E) re-express the cells at 42 °C overnight. - CORRECT ANSWER✅✅B) refold the insoluble fraction using
guanidine.
, You wish to use dialysis to determine if a 30 kDa and 40 kDa protein interact. You should mix both
proteins and place them into dialysis tubing with a ________ kDa cutoff, and test to see if a dimer
remains inside the tubing.
A) 25
B) 30
C) 35
D) 50
E) 75 - CORRECT ANSWER✅✅D) 50
You place a 20 kDa protein and a 50 kDa protein in a dialysis tubing that has a 30 kDa cutoff, and place it
in a beaker with buffer. If these proteins do not interact,
A) both proteins will remain inside of the dialysis tube.
B) the 50 kDa protein will equilibrate with the buffer.
C) the 20 kDa protein will equilibrate with the buffer.
D) both proteins will equilibrate with the buffer. - CORRECT ANSWER✅✅C) the 20 kDa protein will
equilibrate with the buffer.
What is the purpose of adding sodium azide (NaN3) to a protein sample?
A) To act as a cryoprotectant.
B) To reduce carboxyl groups.
C) To prevent microorganism growth.
D) To inhibit proteases.
E) To act as a buffer against changes in pH that fall outside of the range of Tris. - CORRECT
ANSWER✅✅C) To prevent microorganism growth.
Which of the following can be used as a protease inhibitor to prevent protein degradation?
A) Chaotropic salts.
B) EDTA.
C) Propylene glycol.
D) Ammonium sulfate.
