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BIO 170 Ch 18 Control of Gene Expression in Bacteria
Terms in this set (30)
Repica plating is used to isolate mutants that
cannot grow in a particular condition
Why are the genes involved in lactose metabolism considered to be an operon
they all are controlled by the same promoter
In the lac operon, the repressor inhibits transcription when
the repressor is not bound to the inducer
Activators bind to regulatory sequences in
Activators bind to ______ polymerase
How does inducer exclusion control gene expression in the lac operon?
Inducer exclusion controls gene expression in the lac operon by preventing the transport of lactose into the glycolytic pathway when glucose is present in order to only allow the use of glucose.
A regulon is a set of genes controlled by a
one type of regulator of transcription.
Why does E. coli express genes for glycolytic enzymes constitutively?
It expresses them constitutively because they are genes that need to be expressed all the time to produce ATP which is needed all the time so they constantly remain on
Explain the difference between positive and negative control over transcription.
The difference between positive and negative control over transcription is that positive control promotes transcription and increases the frequency of initiation of transcription while negative control of transcription prevents the initiation of transcription and acts a repressor when glucose is present.
Predict what would happen if the lac repressor protein were altered so it could not bind to the inducer.
The repressor would always be bound to DNA.
Predict what would happen to regulation of the lac operon if the lacI gene were moved 50,000 nucleotides upstream of its normal location.
The location of the lacI gene doesn't matter so regulation would be normal
If any of the following hypothetical drugs could be developed, which would be most effective in preventing cholera?
a. a drug that increased the amount of the ToxR activator
b. a drug that blocked the DNA-binding activity of the activator
c. a drug that increased rates of transcription in V. cholerae
d. a drug that increased rates of translation in V.chloerae.
a drug that blocked the DNA-binding activity of the activator since the activator needs to bind to regulatory sequences to activate gene expression, preventing DNA binding would cripple the regulon and prevent cholera.
IPTG is a molecule with a structure very similar to lactose. IPTG can be transported into cells by galactoside perm ease and can bind to the lac repressor protein. However, unlike lactose, IPTG is not broken down by beta galactosidase. Predict what would occur regarding lac operon regulation if IPTG were added to E.coli growth medium containing arabinose and no glucose or lactose.
The lac operon would be strongly induced. Once inside the cell, the IPTG will bind to the repressor, causing it to release from DNA. IPTG cannot be broken down, so its concentration will remain high. Since glucose is absent, there will be no inducer exclusion to prevent IPTG transport through the galactosidase perm ease transporter.
What are the 3 levels of control in bacteria?
Transcription, Translation, and Post-translational control
What does the control of gene expression allow?
allows for bacteria to respond to environmental changes
What is the preferred carbon source?
Glucose; then lactose if glucose is absent
What are constitutive mutants?
a mutated strain that produces a product at all times rather than only under certain conditions.
What happens if theres a mutant in the LacI gene?
theres no repressor protein to bind and block polymerase so high levels of protein are produced along with beta galactosidase and perm ease.
What were the 3 conditions that were used to see if it would trigger beta galactosidase?
Only glucose present had no beta gal, glucose and lactose had no beta gal, and lactose only had high levels of beta gal.
Why were the 3 conditions used to trigger beta galactosidase?
to discover if glucose affects the regulation of it. Discovered that theres some relationship between lactose and beta galactosidase.
What did replica plating prove?
proved that theres some defect in the lactose pathway because cells don't survive with lactose but do with glucose only.
What mutant is in the LacZ gene? Lac Y? LacI?
LacZ mutant are cells that don't work with the indicator. LacY are cells that can't accumulate lactose, and LacI are constitutive mutants.
Why can the LacI gene control LacZ and LacY?
because of the location of the genes
What is the lac repressor?
The LacI gene`
When is expression of the lac repressor present?
When glucose is present
Why is the lac operon turned on only if glucose isn't present?
because lactose is not needed if glucose is present therefore the lac operon is wasted energy if it's turned on when it's not in use
What is an allosteric change?
A change in the shape of the cell or organelle
What are regulons?
gene expression of multiple operons that are controlled at once, used to suppress expression or promote it.
Where is the Ara operon found? What does it do?
It's found it plant cell walls and it is transcribed when it's present but not transcribed when its not present.
What does the lacZ gene encode? LacY?
the gene encodes beta galactosidase and the second encodes galactoside perm ease
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