Biology 151 Exam 3 Rated A+ New
Update
Why are the genes involved in lactose metabolism considered to be part of an operon?
A. They occupy adjacent locations on the E. coli chromosome
B. They have a similar function
C. They are under the control of the same promoter - Answer ✔✔- c
True of False? Lactose is the preferred energy source in E. coli. - Answer ✔✔- False
Predict the phenotype of a lacI promoter mutant, which has mutation in the promoter of
the lacI gene (LOF).
A The lac genes would only be expressed efficiently in the presence of lactose
B. The lac genes would only be expressed efficiently in the absence of lactose
C. The lac genes would be constitutively expressed
D. The lac genes would never be expressed efficiently - Answer ✔✔- This mutant would
result in no lacI repressor being made so it wouldn't be able to repress transcription of
the lac operon
C
Predict the phenotype for a lacY mutant, which has a loss-of-function mutation in the
gene for permease.
A. The lac genes would only be expressed efficiently in the presence of lactose
B. The lac genes would only be expressed efficiently in the absence of lactose
C. The lac genes would be constitutively expressed
D. The lac genes would never be expressed efficiently - Answer ✔✔- If no permease,
no lactose getting into the cell so no lactose binding to repressor
D
The Lac repressor binds to a specific DNA sequence in the lacO operator region of the
lac operon. Predict the phenotype if you changed the sequence of the lacO operator.
A. The lac genes would only be expressed efficiently in the presence of lactose
B. The lac genes would only be expressed efficiently in the absence of lactose
C. The lac genes would be constitutively expressed
D. The lac genes would never be expressed efficiently - Answer ✔✔- Repressor can't
bind to no repression of transcription
C
Which of the following mutations would leave E. coli unable to use lactose as a sugar
source?
6. Change the sequence of the lac operator (lacO)
, 7. A disruption in the promoter of the lacI gene
8. A loss of function mutation in the lacY gene (permease protein)
9. A gain of function mutation in adenylate cyclase (the enzyme that makes cAMP) -
Answer ✔✔- B
B
A
B
For the E. coli lac operon, when lactose is present:and glucose is absent, cAMP binds
and activates CAP - Answer ✔✔- yes
For the E. coli lac operon, when lactose is present:activated CAP binds the repressor
protein to remove it from the operator gene - Answer ✔✔- no
For the E. coli lac operon, when lactose is present the cell prefers lactose over glucose -
Answer ✔✔- I'll accept either answer for this question - a little ambiguous, but the
answer is no, the cell never PREFERS lactose over glucose but if there's lactose but no
glucose present then it will certainly be happy enough to break down the lactose to use
as an energy source.
For the E. coli lac operon, when lactose is present:and glucose is present, repressor will
not be bound to the operator the majority of the time - Answer ✔✔- yes because lactose
is present
For the E. coli lac operon, when lactose is present: RNA polymerase cannot bind to the
promoter - Answer ✔✔- no
A type of DNA sequence in eukaryotes that helps to regulate transcription, may be
tissue specific, and may exert control over a gene that is a great distance away is called
A. A silencer
B. An operator
C. A TATA box
D. An enhancer
E. More than one of the above - Answer ✔✔- E. More than one of the above A and D
A type of DNA sequence in eukaryotes that helps to regulate transcription, is not tissue
specific, and is required for RNA polymerase binding to the promoter is called
A. A silencer
B. An operator
C. A TATA box
D. An enhancer
E. More than one of the above - Answer ✔✔- C. A TATA box
Activation of a eukaryotic gene typically involves:
A. Release of transcription factors from the gene's promoter
Update
Why are the genes involved in lactose metabolism considered to be part of an operon?
A. They occupy adjacent locations on the E. coli chromosome
B. They have a similar function
C. They are under the control of the same promoter - Answer ✔✔- c
True of False? Lactose is the preferred energy source in E. coli. - Answer ✔✔- False
Predict the phenotype of a lacI promoter mutant, which has mutation in the promoter of
the lacI gene (LOF).
A The lac genes would only be expressed efficiently in the presence of lactose
B. The lac genes would only be expressed efficiently in the absence of lactose
C. The lac genes would be constitutively expressed
D. The lac genes would never be expressed efficiently - Answer ✔✔- This mutant would
result in no lacI repressor being made so it wouldn't be able to repress transcription of
the lac operon
C
Predict the phenotype for a lacY mutant, which has a loss-of-function mutation in the
gene for permease.
A. The lac genes would only be expressed efficiently in the presence of lactose
B. The lac genes would only be expressed efficiently in the absence of lactose
C. The lac genes would be constitutively expressed
D. The lac genes would never be expressed efficiently - Answer ✔✔- If no permease,
no lactose getting into the cell so no lactose binding to repressor
D
The Lac repressor binds to a specific DNA sequence in the lacO operator region of the
lac operon. Predict the phenotype if you changed the sequence of the lacO operator.
A. The lac genes would only be expressed efficiently in the presence of lactose
B. The lac genes would only be expressed efficiently in the absence of lactose
C. The lac genes would be constitutively expressed
D. The lac genes would never be expressed efficiently - Answer ✔✔- Repressor can't
bind to no repression of transcription
C
Which of the following mutations would leave E. coli unable to use lactose as a sugar
source?
6. Change the sequence of the lac operator (lacO)
, 7. A disruption in the promoter of the lacI gene
8. A loss of function mutation in the lacY gene (permease protein)
9. A gain of function mutation in adenylate cyclase (the enzyme that makes cAMP) -
Answer ✔✔- B
B
A
B
For the E. coli lac operon, when lactose is present:and glucose is absent, cAMP binds
and activates CAP - Answer ✔✔- yes
For the E. coli lac operon, when lactose is present:activated CAP binds the repressor
protein to remove it from the operator gene - Answer ✔✔- no
For the E. coli lac operon, when lactose is present the cell prefers lactose over glucose -
Answer ✔✔- I'll accept either answer for this question - a little ambiguous, but the
answer is no, the cell never PREFERS lactose over glucose but if there's lactose but no
glucose present then it will certainly be happy enough to break down the lactose to use
as an energy source.
For the E. coli lac operon, when lactose is present:and glucose is present, repressor will
not be bound to the operator the majority of the time - Answer ✔✔- yes because lactose
is present
For the E. coli lac operon, when lactose is present: RNA polymerase cannot bind to the
promoter - Answer ✔✔- no
A type of DNA sequence in eukaryotes that helps to regulate transcription, may be
tissue specific, and may exert control over a gene that is a great distance away is called
A. A silencer
B. An operator
C. A TATA box
D. An enhancer
E. More than one of the above - Answer ✔✔- E. More than one of the above A and D
A type of DNA sequence in eukaryotes that helps to regulate transcription, is not tissue
specific, and is required for RNA polymerase binding to the promoter is called
A. A silencer
B. An operator
C. A TATA box
D. An enhancer
E. More than one of the above - Answer ✔✔- C. A TATA box
Activation of a eukaryotic gene typically involves:
A. Release of transcription factors from the gene's promoter
