Gene regulation Flashcards
How do cells maintain and regulate their metabolism ?
- Regulation of the enzymatic activity (activation/inhibtion)
- Regulation of the enzyme synthesis (gene expression)
Feedback loop is an example of what type of metabolic regulation ?
Regulation of the enzymatic activity
What’s an operon
Unit of genetic function found in bacteria, consisting of a promoter, an operator and a coordinately regulated cluster of genes whose products function in a common pathway
What part of an operon is refered to as the ON/OFF switch ?
Operator
Under normal conditions, the trpR repressor is ___
inactive
How can the trpR repressor be activated ?
If tryptophan binds to it
What is a corepressor ? name an example
Tryptophan : it cooperates with a repressor to turn the operon off (the one that activates the repressor)
Under normal conditions, is the trp operon on or off ?
On
Operon is switched off by a « trp »___ that binds to the operator
repressor
The operator controls what ?
The access of the RNA pol to the genes
When active, does the repressor activate or repress gene expression ?
Repress
a repressor represents what kind of gene regulation ?
Negative control
When tryptophan is absent, the repressor is __ and the operon is ___
repressor is inactive
Operon is on
(transcription is active)
When tryptophan is present, the repressor is __ and the operon is __
Repressor is active
Operon is off
(no transcription)
Explain the steps to negative regulation of the tryptophan synthesis
- Lots of tryptophan
- Tryptohan activates the trp repressor
- RNA pol II cannot do transcription of tryptophan
- Decrease of the tryptophan pathway enzymes
- Decrease of tryptophan synthesis
What type of control is typical of anabolic pathways ?
Negative control through repressible operon (trp example –> operon is normally on and can be inhibited by repressor)
What is an inducible operon ?
Operon that is usually off and can be activated (induced/stimulated)
Name an example of an inducible operon
Lac operon :
When lactose is absent, it the repressor is active (operon is off –> no transcription)
When lactose is present, it inactivates the repressor (operon is on –> transcription)
(lactose is the inducer –> stimulates activity of the operon)
What type of control is typical of catabolic pathways ?
negative control through an inducible operon (lactose example –> operon is normally off and can be activated by an inducer)
true or false : both repressible and inducible operons are 2 types of negative genes regulations
true
Describe how the lac operon is also under a positive control
When cAMP receptor protein (CRP) binds to the lac promoter, it increases the affinity to the RNApol (which is responsible for transcription)
–> The presence of CRP increases gene transcription of the lac operon
With the lac operon example, what happens if both glucose and lactose are present in the cell ?
The presence of glucose inhibits the adenylyl cyclase
–> decrease in cAMP
–> CRP detaches from the lac promoter
–> RNApol has less affinity for the promoter
–> decrease of the lac operon gene expression (no transcription)
Because we’d rather juste use the glucose present as a source of energy instead of converting lactose into glucose and galactose (would be more expensive energy wise)
in which of the following scenarios would the lac operon be ON ?
- + glucose, + lactose
- + glucose, - lactose
- - glucose, - lactose
- - glucose, + lactose
- -glucose, + lactose
(because when glucose is present, we use it as energy instead of converting the lactose into glucose and galactose)
(and if there’s no lactose and no glucose, the operon is off because it is an inducible operon and lactose is the inducer)
Name all the stages where gene expression can be modulated
- Transcription, RNA processing, translation, Post translation modifications and degradation
- Turned ON/OFF
- Accelerated/slowed down
- Coordinated
