Regulation of Bacterial Gene Expression Flashcards
Why can polycistronic mRNAs be translated into several different protein products and why is this important?
Ribosomes can bind to internal Shine-Dalgarno sites
Good mechanism for making equal amounts of related protein products
What is a regulon?
Structural genes that participate in a single pathway that are scattered at different sites in the genome that contain similar controlling elements so that they are expressed coordinately
Describe the two types of negative control.
Negative inducible - ligand inactivates repressor
Negative repressible - ligand activates repressor
*Negative control always involves a repressor
Describe the two types of positive control.
Positive inducible - coactivator ligand activates an activator protein
Positive repressible - ligand inactivates activator protein
What will occur in the lac operon in the presence of glucose but no lactose?
No lactose means repressor is bound and operon is not functional
What will occur in the lac operon in the presence of lactose but no glucose?
Allolactose binds and inactivates repressor
cAMP (due to low glucose) binds CAP and further activates the operon
What will occur in the lac operon in the presence of glucose and lactose?
Allolactose will inactivate repressor
CAP won’t be active due to low cAMP levels, so only partial activation will occur
What is diauxic growth?
The sequential use of carbon sources
E.g. glucose is used before lactose in E. coli
What are the roles of the PTS system in sugar metabolism?
Transport sugars across inner membrane
Under low glucose, P-IIIglc activates adenylate cyclase producing cAMP
IIIglc turns off nonPTS sugar transport systems
PTS serves as part of the sensing mechanism for chemotaxis
What is two-component regulation of gene expression?
One protein component acts as a membrane sensor that detects environmental signals
The other protein is a transcriptional activator or repressor (e.g. CAP)
What is Quorum Sensing?
A mechanism by which a set of genes are activated when the concentration of bacteria reaches a threshold
What is global regulation?
The control of multiple metabolic pathways by a single regulator
E.g. cAMP binding protein
