Chapter 18: Gene Expression in Bacteria Flashcards
What is the preferred energy source for E. coli always?
Glucose > all
What is tryptophan in the trp operon?
A corepressor
In an operon, where RNA polymerase can bind and begin transcription
Promoter
How is the trp repressor activated?
Tryptophan binds to it
Does the lac operon get activated when lactose is present but glucose is not low?
Yes, it just transcribes more slowly. Less glucose leads to faster transcription
Usually turned off but can be switched on
Inducible
How does transcription proceed in an operon?
When the repressor protein leaves
In operon, can be within the promoter or between the promoter and the genes
Operator
How does the E. coli cell know when to start using lactose as energy?
cAMP accumulates when glucose is scarce and cAMP activates CAP (catabolic activator protein) which binds to lac promoter and increases the affinity of RNA polymerase for the promoter. This increases the rate of transcription
How is gene expression controlled?
Genes can be turned on and off or the level of expression can vary
What happens in the trp operon when tryptophan is present?
Tryptophan binds to the repressor and activates it and can then bind to operator to block polymerase turning the operon off
When does E. coli start to use lactose as energy?
When glucose is low in supply
3 components of operons
Promoter, operator, and structural genes
Set of separate genes (or operons) controlled by a single regulatory protein
Regulon
What is the normal state of a lac operon?
Repressor (coded for by lacI) is active by itself
Contains the genes which code for the enzymes needed to synthesize tryptophan
Trp operon
Example of a regulon
ToxT in cholera activates many genes
Why do bacteria need to switch genes off and on? Example?
Respond to changing environments. E. coli in colon synthesize tryptophan when its not in diet and don’t when it is in diet
Usually turned on but can be inhibited
Repressible
How is the trp repressor made?
It is coded for by the regulatory gene (trpR) which is not part of the operon
In operon, segment of DNA that acts as the on/off switch where repressor binds
Operator
What does turning genes off and on do for bacteria?
Makes them the most efficient
What happens when lactose is present in a lac operon?
Lactose inactivates the repressor and the operon is on
What happens in the trp operon when there is no tryptophan?
The trp operon is on and synthesizing tryptophan
How is the trp operon shut off?
Trp repressor binds to operator to block polymerase. Occurs in the abundance of product
What does less glucose lead to in the lac operon?
Less glucose leads to faster transcription
Contains genes which code for enzymes necessary to transport and metabolize lactose
Lac operon
What happens if bacteria need to coordinate a large number of genes?
Alternative sigma proteins and regulons
Is the lac operon inducible or repressible?
Inducible
Is the trp operon inducible or repressible?
Repressible
In operon, the genes that are co-regulated
Structural genes
Where can gene expression control occur?
Transcription, Translation, and post-translation
What happens when there is no lactose present in a lac operon?
Repressor is active and bund to the operator, turning it off
Process of converting information stored in DNA into active gene product (protein)
Gene expression
Cluster of co-transcribed genes with related functions in bacteria
Operons
What is the inducer in the lac operon?
Allolactose or lactose (substrates)
What is needed to activate a lac operon?
An inducer is needed to bind and inactivate the repressor
