Transcriptional Regulation - Prokaryotes Flashcards
Why is transcriptional regulation the most common form of regulation?
It is the most efficient
What is the major mechanism of transcriptional regulation?
Regulation of the recruitment of RNA polymerase, either by repressing or promoting binding to the promotor
What proteins physically block RNA polymerase from binding to stop transcription?
Repressor proteins
How do prokaryotes regulate networks of genes?
Operons
What are operons?
Clusters of genes transcribed as a single transcript
Why do operons allow for regulation of networks of genes?
Since they all work together, transcribing them into a single mRNA mean they are also all regulated together at the same time
Where is the lux operon found?
Vibrio fischeri, bioluminescent bacteria
What does the lux operon produce? How many genes are there?
5 proteins are expressed. Two make up luciferase, the fluorescent protein, and the other three are fatty acid reductases
How is the lux operon regulated?
By an activator: LuxR
What regulates whether the lux operon activator binds?
The amount of autoinducer around
What are autoinducers?
Small molecules secreted by bacteria that tell other bacterial cells how many there are around
Why are autoinducers required for the lux operon?
LuxR can’t bind to DNA unless it is bound to an autoinducer
When does the lux operon get expressed?
When there is a lot of autoinducer around at high cell density
How much of the lux operon is being transcribed at low cell density?
Transcription is off. There is little autoinducer around, so LuxR can’t bind to DNA to activate transcription
How much of the lux operon is being transcribed at high cell density?
Transcription is on. There is a lot of autoinducer, so LuxR can bind to DNA and activate transcription
Where is the Lac operon found?
E. coli
What is the Lac operon used for?
Lactose metabolism
How is the Lac operon regulated?
With both an activator and a repressor
What are the 4 genes in the Lac operon?
LacZ, LacI, LacA and LacY
What is the function of the LacZ gene?
Encodes for beta-galactosidase, the enzyme that cleaves lactose into glucose and galactose
What is the function of the LacI gene?
Encodes for the repressor
What is the function of the LacY gene?
Encodes for lactose permease, the transport protein that lets lactose into the cell
What is the function of the LacA gene?
Encodes a transacetylase and is involved in side reactions from beta-galactosidase
Which of the 4 Lac operon genes is independently expressed?
LacI - the repressor
What is the activator of the Lac operon?
CAP
Where does the Lac operon activator bind? What does it do?
Binds to the CAP site in the regulatory region of the operon. It helps RNA polymerase bind but their binding sites don’t overlap
Where does the Lac operon repressor bind? What does it do?
Binds to the operator. It overlaps with the binding site of RNA polymerase and physically blocks it from binding
What is the basal state of a promotor?
The level of expression when the gene is not being regulated in any way
Is the basal state of a gene the same for every gene?
No, it changes depending on the strength of the promotor
What is the basal state of the Lac operon?
Low transcription
What is the level of transcription when only the repressor is bound to the Lac operon?
Off
What is the level of transcription when only the activator is bound to the Lac operon?
High
What is the level of transcription when both the repressor and the activator is bound to the Lac operon?
Off. The repressor is physically blocking RNA polymerase, so it wins out
What molecule regulates the activity of the Lac operon repressor?
Lactose
What molecule regulates the activity of the Lac operon activator?
Indirect regulation by glucose, which is inversely proportional to the levels of cAMP
Is the Lac operon repressor active or inactive when lactose levels are high?
Inactive
Is the Lac operon repressor active or inactive when lactose levels are low?
Active
Is the Lac operon activator active or inactive when glucose levels are high?
Inactive
Is the Lac operon activator active or inactive when glucose levels are low?
Active
How does glucose regulate the activity of the Lac operon activator?
It is indirect through cAMP. cAMP binds directly to the activator
How much cAMP is present when glucose levels are high?
Low
How much cAMP is present when glucose levels are low?
High
