Topic 10 Trp Operon Flashcards
Lactose is a _____
Tryptophan is a ______
What does this mean
Sugar
Amino acid
Cell can make trip by itself but would prefer it from the environment
When is the trp operon turned on, how is this diff from the lac operon
On when tryptophan’s isn’t available from the environment
The lac is on when lactose is present in environment
What is the goal of the trip operon and what is the order of genes
To make trp
P O trpE trpD trpC trpB trpA
How is trp operon expression regulated
Through negative regulation and
attenuation (after transcription has started)
How does the negative regulation of trp work in presence of tryptophan
Tryptophan (allosteric effector) binds to the TrpR repressor, this lets it bind to the trpO (the operator)
Causes transcription to be stopped
How does the negative regulation of trp work in absence of tryptophan or low lvls
TrpR (repressor) can’t bind to trpO (operator) since no tryptophan
So transcription occurs
What is attenuation
Extra boost of repression, decrease in mRNA production when there is lots of tryptophan
Effect the operon AFTER transcription has started
Involves the leader sequence (162bp) long
Where is the leader sequence
Between O ant trpE
In the leader sequence, what is the first impoertant section
How many amino acids long
The first section is the leader peptide trpL
14 amino acid peptide
Has 2 UGG codons that encode tryptophan (rarest amino acid in proteins)
In the leader sequence, what is the 4th impoertant section
The attenuator region at the end of the leader sequence
What does the mRNA leader sequence do
Make stem loops structure , has four regions
But only two region are forming a loop together at one time
How does attenuation work when there is high tryptophan level
Lots of tRNA attached to tryptophan,
Ribosome for translation attached to newly made mRNA while rna pol is transcribing
Ribosome binds and translates region one of leader sequence that has UGGUGG then moves to region 2
Moving to region two makes regions 3 and 4 form a stem loop which stops transcription, making rna pol fall off
This level of tryptophan favours transcription termination where the structural genes don’t get transcribed
How does attenuation work when there is low tryptophan level
Want to make trp
Ribosome attached to region one and stalls there
This makes region 2 and 3 loop
This causes no termination of transcription from rna pol since ribosome didn’t move to region 2 and form the other loop
The UGGUGG region only regulates transcription, stall ribosome or not stall ribosome
The protiens for trp operon are made
What is factor independent termination?
Where does it happen in trp operon
RNA pol transcribes a stem loops followed by a string of u’s which terminates transcription
The 3-4 stem loop is followed by a string of U
