Control of Gene Expression in Bacteria Flashcards
What are constitutively expressed genes
genes that specify gene products essential for living cells, that are continuously expressed in most cells
What are inducible and repressible genes
some gene products are only needed under certain conditions, so regulatory mechanisms allow synthesis of these gene products only when needed (inducible) or shut down genes when no longer needed (repressible)
What level of regulation is the concern in this course
regulation at the level of transcription initiation
What is required of regulation in the initiation transcription level
binding of proteins (transcription factors) to the DNA
What are DNA binding proteins in relation to gene regulation in transcription initiation
can be activators or repressors
- contain domains that recognize DNA sequences in combination with grooves in DNA
- non covalent bonding
- bind to the promoter of a gene
- recruits RNA polymerase
Transcription in bacteria is regulated by _____________
operons
Regulation of transcription is controlled by ___________ _______________
regulator proteins
*and the promoter/operator complex
Where do regulator proteins bind
the promoter (or operon)
What is the function of negative regulatory proteins
inhibit transcription
What is the function of positive regulator proteins
active transcription
What are inducible operons
transcription of the operon is normally off, and something happens to turn it on
What are repressible operons
transcription of the operon is normally on, and something happens to turn it off
How does a regulator protein function to keep transcription turned off (negative inducible operon)
blocks the binding of RNA polymerase
How can transcription involving a negative inducible operon be restored if being repressed
a small molecule called an inducer binds to the inhibitor/repressor and inactivates it, so the repressor can no longer bind to DNA and RNA poly can activate transcription
How does a regulator protein function to turn off transcription (negative repressible operon)
can’t bind to the promoter/operator complex without a cofactor (repressor is inactive in the absence of a cofactor)
- small molecule called a corepressor binds to the repressor and allows the repressor/corepressor complex to bind to the operator to inhibit transcription
How does a regulator protein function to positively control transcription
regulatory protein is an activator (think positive) and binds to operator to induce txn
- binds upstream of promotor an enhances the binding of RNA poly to the promoter
What is an example of a positive activator of transcription
catabolite activator protein (CAP) is a positive activator of transcription
In relation to the Lac operon, how does negative inducible control occur
regulator is an inhibitor
allolactose inactivates inhibitor
In relation to the Lac operon, how does positive control occur
CAP+cAMP enhances transcription
What is coordinate induction
the simultaneous synthesis of several proteins by a specific molecule called the inducer
What are the three enzymes in the operon involving metabolism of lactose via E. coli
Permase (lacY)
B-galatosidase (lacZ)
thiogalactoside transacetylase (lacA)
Read the slides about the Lac operon and understand them*****
see slides 18-20 in “control of gene expression in bacteria” slideshow
What is cis regulation
control gene expression only on the same piece of DNA
What is trans regulation
control gene expression of other DNA molecules
The promoter sequence for the operon is ___________ acting on lacZ
cis
The repressor protein is ____________ acting on lacZ
trans
Non functional mutations are noted with what symbol
”-“
Functional mutations are noted with what symbol
”+”
Why is glucose the preferred source of energy in bacteria
it is easier to metabolize
When glucose is present, bacteria will turn off other pathways; this is called…
catabolite repression
Positive glucose metabolism in bacteria resulting in repression of other pathways; this is called…
positive control
Levels of __________ are inversely proportional to glucose levels
cAMP
If glucose is low, cAMP is
high
and vice versa
Since levels of cAMP impact expression of lac operon, when glucose is high and cAMP is low, what happens to lac operon expression
significantly reduced
(due to reduced affinity of poly to promoter)
