Prokaryotic Regulation Flashcards
Negative Regulation
any regulation of gene expression
when a protein binding to DNA has a negative effect on the
expression of the gene. E.g., binding of either the lac
repressor OR the trp repressor to the operator, inhibits RNA
polymerase transcription.
Positive Regulation
any regulation of gene expression that
when a protein binding to DNA has a positive effect on the
expression of the gene. E.g., binding of the CAP-cAMP
complex enhances the binding of RNA polymerase to the
promoter and has a positive effect on transcription.
Positive regulation of the lac operon:
cAMP present vs not present
present: cAMP binds to CAP and the
cAMP-CAP complex binds
to DNA at the CAP site.
RNA polymerase binds
the promoter efficiently.
Transcription occurs frequently.
not: CAP does not bind to DNA.
RNA polymerase binds
the promoter inefficiently.
Transcription occurs rarely.
cAMP & glucose relationship
The amount of cAMP and the rate of transcription of the lac operon are inversely related to the concentration
of glucose.
Full expression of lac operon requires:
“relieving” of
negative regulation:
-the release of the lac repressor
-occurs in the presence of lactose
and
the “application” of positive regulation:
-the binding of CAP-cAMP
-occurs in the absence of glucose
Glucose inhibits transcription of the lac operon by _____.
a. strengthening the binding of the repressor to the operator
b. reducing levels of intracellular cAMP
c. inhibiting RNA polymerase from opening the strands of DNA to initiate
transcription.
d. weakening the binding of repressor to the operator
B
What happens to the expression of the lacI gene if lactose is not available in
the cell?
a. The lacI gene turns off.
b. The lacI gene turns on.
c. The lacI gene increases its rate of transcription.
d. There is no change in lacI gene expression.
D
Galactoside permease
transports lactose into the cell.
β-Galactosidase
breaks down lactose inside the cell.
Operon
a unit of bacterial DNA that contains
a cluster of genes under the control of a single
promoter.The expression of these genes are also under the control of a single operator.
lacI
Prevents transcription
of lacZ and lacY when
lactose is absent
Suppose an experimenter creates a technique that allows her to move DNA sequences within a prokaryotic genome.
If she moves the operator to a position just after the protein-coding genes, which of the following would likely occur?
a. The repressor will no longer bind to the operator.
b. The structural genes will be transcribed continuously.
c. The operon will never be transcribed.
d. The repressor protein will no longer be produced.
e. The inducer will no longer bind to the repressor.
B
An experimenter creates a technique that allows her to move DNA sequences within a prokaryotic genome.
If she moves the repressor gene (lacI), along with its promoter, to a position at some several thousand base
pairs away from its normal position, which will you expect to occur?
a. The lac operon will be expressed continuously.
b. The repressor will no longer bind to the inducer.
c. The repressor will no longer bind to the operator.
d. The lac operon will function normally.
e. The repressor will no longer be made.
D
Forms of control in bacteria
Transcriptional (saves most energy for the cell), Translational (allows more rapid changes) , Post Translation (most rapid response)
Translational control
The cell could prevent mRNAs for unneeded proteins from being translated.
