BIOLOGY 203 EXAM 4 QUESTIONS
AND ANSWERS 100% SOLVED 2025
,Which of the following is a protein produced by a regulatory gene?
A) operon
B) inducer
C) promoter
D) repressor - ANSWERD) repressor
A lack of which molecule would result in a cell's inability to "turn off" genes?
A) operon
B) inducer
C) promoter
D) corepressor - ANSWERD) corepressor
Which of the following, when taken up by a cell, binds to a repressor so that the
repressor no longer binds to the operator?
A) inducer
B) promoter
C) repressor
D) corepressor - ANSWERA) inducer
Most repressor proteins are allosteric. Which of the following binds with the repressor to
alter its conformation?
A) inducer
B) promoter
C) transcription factor
D) cAMP - ANSWERA) inducer
A mutation that inactivates a regulatory gene of a repressible operon in an E. coli cell
would result in _____.
A) continuous transcription of the structural gene controlled by that regulator
B) complete inhibition of transcription of the structural gene controlled by that regulator
C) irreversible binding of the repressor to the operator
D) continuous translation of the mRNA because of alteration of its structure -
ANSWERA) continuous transcription of the structural gene controlled by that regulator
The lactose operon is likely to be transcribed when _____.
A) there is more glucose in the cell than lactose
B) there is glucose but no lactose in the cell
C) the cyclic AMP and lactose levels are both high within the cell
D) the cAMP level is high and the lactose level is low - ANSWERC) the cyclic AMP and
lactose levels are both high within the cell
Transcription of structural genes in an inducible operon _____.
, A) occurs continuously in the cell
B) starts when the pathway's substrate is present
C) starts when the pathway's product is present
D) stops when the pathway's product is present - ANSWERB) starts when the
pathway's substrate is present
For a repressible operon to be transcribed, which of the following must occur?
A) A corepressor must be present.
B) RNA polymerase and the active repressor must be present.
C) RNA polymerase must bind to the promoter, and the repressor must be inactive.
D) RNA polymerase must not occupy the promoter, and the repressor must be inactive.
- ANSWERC) RNA polymerase must bind to the promoter, and the repressor must be
inactive.
Altering patterns of gene expression in prokaryotes would most likely serve an
organism's survival by _____.
A) organizing gene expression, so that genes are expressed in a given order
B) allowing each gene to be expressed an equal number of times
C) allowing an organism to adjust to changes in environmental conditions
D) allowing environmental changes to alter a prokaryote's genome - ANSWERC)
allowing an organism to adjust to changes in environmental conditions
In positive control of several sugar-metabolism-related operons, the catabolite activator
protein (CAP) binds to DNA to stimulate transcription. What causes an increase in CAP
activity in stimulating transcription?
A) an increase in glucose and an increase in cAMP
B) a decrease in glucose and an increase in cAMP
C) an increase in glucose and a decrease in cAMP
D) a decrease in glucose and a decrease in the repressor - ANSWERB) a decrease in
glucose and an increase in cAMP
There is a mutation in the repressor that results in a molecule known as a super-
repressor because it represses the lac operon permanently. Which of these would
characterize such a mutant?
A) It cannot bind to the operator.
B) It cannot make a functional repressor.
C) It cannot bind to the inducer.
D) It makes a repressor that binds CAP. - ANSWERC) It cannot bind to the inducer.
If she moves the promoter for the lac operon to the region between the beta
galactosidase (lacZ) gene and the permease (lacY) gene, which of the following would
be likely?
A) The three structural genes will be expressed normally.
B) RNA polymerase will no longer transcribe permease.
C) The operon will still transcribe the lacZ and lacY genes, but the mRNA will not be
translated.
AND ANSWERS 100% SOLVED 2025
,Which of the following is a protein produced by a regulatory gene?
A) operon
B) inducer
C) promoter
D) repressor - ANSWERD) repressor
A lack of which molecule would result in a cell's inability to "turn off" genes?
A) operon
B) inducer
C) promoter
D) corepressor - ANSWERD) corepressor
Which of the following, when taken up by a cell, binds to a repressor so that the
repressor no longer binds to the operator?
A) inducer
B) promoter
C) repressor
D) corepressor - ANSWERA) inducer
Most repressor proteins are allosteric. Which of the following binds with the repressor to
alter its conformation?
A) inducer
B) promoter
C) transcription factor
D) cAMP - ANSWERA) inducer
A mutation that inactivates a regulatory gene of a repressible operon in an E. coli cell
would result in _____.
A) continuous transcription of the structural gene controlled by that regulator
B) complete inhibition of transcription of the structural gene controlled by that regulator
C) irreversible binding of the repressor to the operator
D) continuous translation of the mRNA because of alteration of its structure -
ANSWERA) continuous transcription of the structural gene controlled by that regulator
The lactose operon is likely to be transcribed when _____.
A) there is more glucose in the cell than lactose
B) there is glucose but no lactose in the cell
C) the cyclic AMP and lactose levels are both high within the cell
D) the cAMP level is high and the lactose level is low - ANSWERC) the cyclic AMP and
lactose levels are both high within the cell
Transcription of structural genes in an inducible operon _____.
, A) occurs continuously in the cell
B) starts when the pathway's substrate is present
C) starts when the pathway's product is present
D) stops when the pathway's product is present - ANSWERB) starts when the
pathway's substrate is present
For a repressible operon to be transcribed, which of the following must occur?
A) A corepressor must be present.
B) RNA polymerase and the active repressor must be present.
C) RNA polymerase must bind to the promoter, and the repressor must be inactive.
D) RNA polymerase must not occupy the promoter, and the repressor must be inactive.
- ANSWERC) RNA polymerase must bind to the promoter, and the repressor must be
inactive.
Altering patterns of gene expression in prokaryotes would most likely serve an
organism's survival by _____.
A) organizing gene expression, so that genes are expressed in a given order
B) allowing each gene to be expressed an equal number of times
C) allowing an organism to adjust to changes in environmental conditions
D) allowing environmental changes to alter a prokaryote's genome - ANSWERC)
allowing an organism to adjust to changes in environmental conditions
In positive control of several sugar-metabolism-related operons, the catabolite activator
protein (CAP) binds to DNA to stimulate transcription. What causes an increase in CAP
activity in stimulating transcription?
A) an increase in glucose and an increase in cAMP
B) a decrease in glucose and an increase in cAMP
C) an increase in glucose and a decrease in cAMP
D) a decrease in glucose and a decrease in the repressor - ANSWERB) a decrease in
glucose and an increase in cAMP
There is a mutation in the repressor that results in a molecule known as a super-
repressor because it represses the lac operon permanently. Which of these would
characterize such a mutant?
A) It cannot bind to the operator.
B) It cannot make a functional repressor.
C) It cannot bind to the inducer.
D) It makes a repressor that binds CAP. - ANSWERC) It cannot bind to the inducer.
If she moves the promoter for the lac operon to the region between the beta
galactosidase (lacZ) gene and the permease (lacY) gene, which of the following would
be likely?
A) The three structural genes will be expressed normally.
B) RNA polymerase will no longer transcribe permease.
C) The operon will still transcribe the lacZ and lacY genes, but the mRNA will not be
translated.
