Chapter 18: Control of Gene Expression in Bacteria Flashcards
What are the 3 mechanisms of regulation in bacteria?
- transcriptional control
- translational control
- post-translational control
What is transcriptional control?
stops between DNA to mRNA
- changes mRNA lifespan
What is translational control?
stops between mRNA to protein
- changes rate of translation
What is post-translational control?
stops between protein to activated protein
- removes phosphate
What does galactoside permease do?
transports lactose into the cell
What does B-galactosidase do?
breaks down lactose
What is an inducer?
small molecule that initiates transcription
What did Jacob and Monod do?
- generate random mutations in E. coli
- study mutants with defects in lactose metabolism
What do lacZ and lacY code for?
enzymes involved in metabolism
What is lacI responsible for?
regulation of other genes
What is an operon?
set of coordinately regulated bacterial genes that are transcribed together into one mRNA
DEscribe negative control
repressor protein binds to DNA and shuts down transcription (on/off switch)
Describe positive control
activator protein binds to DNA and triggers transcription (volume control)
Describe the lac operon in its “off” state.
- default state
- lacI codes for the repressor protein
- repressor binds to the operator to prevent transcription
- dna sequence that overlaps with the promoter region
Describe the lac operon in its “on” state
- lactose (inducer) binds to the repressor
- repressor changes shape, can no longer bind to DNA (allosteric regulation)
When is the lac operon off?
when lactose is absent in the cell
- the repressor is bound to DNA and transcription stops
When is the lac operon on?
when lactose is present in the cell
- lactose inducer binds to the repressor, repressor releases from DNA and transcription occurs
When lactose is present, but lacI is mutated, what happens?
constitutive expression
What is CAP?
- catabolite activator protein
- when bound to cAMP (second messenger), binds to DNA to increase transcription
When is cAMP produced?
when glucose concentration is low
High glucose concentration = __________ = _____________
low cAMP = low transcription of lac operon
What is inducer exclusion?
glucose inhibits the activity of galactoside permease
- prevents lactose from entering the cell
What is the trp operon?
- alternative negative control
- negative control of an anabolic pathway (synthesis of the amino acid tryptophan)
- transcription happens when trp is absent
How do you turn off the trp operon?
- default is on
Off:
- trp co-repressor binds to the repressor
- repressor changes shape, now able to bind DNA
