Chapter 12: Regulation of Gene Expression in Bacteria and Bacteriophage Flashcards
What are three examples of transcriptional regulation?
Inducible regulation - lac operon
repressible transcription - trp operon
attenuation - trp operon and riboswitches
What is constitutive transcription?
Constitutive genes are always transcribed
What is regulated transcription?
proteins are only produced when the system needs it
What is an inducible operon?
Genes must be turned on
default state = no transcription
ex: when substrate is present
What is a repressible operon?
Genes must be turned off
always transcribed unless turned off
ex: when sufficient product is present
What are the players of negative control of transcription?
Repressor
inducer OR corepressor
Describe the effect of inducer in negative regulation
Binding of repressor protein blocks transcription
binding of inducer molecule to repressor protein allows transcription to occur
Describe the effect of corepressor in negative regulation
binding of repressor-corepressor complex blocks transcription by negative regulation
with corepressor absent, repressor does not bind, allowing transcription
What are the players of positive control of transcription?
Activator
effector OR allosteric inhibitor
Describe the effect of allosteric effector compound in positive regulation?
Absense of effector prevents activator protein binding and transcription
effector binding to activator protein activates transcription by positive regulation
Describe the effects of allosteric inhibitor compound in positive regulation?
Binding of inhibitor to activator protein prevents activator binding and transcription
absense of inhibitor allows binding of activator protein and activates transcription
brief summary of lactose metabolism
Permease helps lactose into the cell
lactose is a disaccharide, must be broken down into two glucose by galactoside linkage
some lactose is changed to allolactose by B-galactosidase
What genes make up the structural region of the Lac Operon?
LacZ
LacY
LacA
What makes up the regulation region of the Lac Operon?
CAP binding site
lac operon promoter
operator
(lacl)???
What enzyme is coded for by LacZ?
B-galactosidase
What enzyme is coded for by LacY?
Permease
What enzyme is coded for by LacA?
Transacetylase
Describe the purpose of negative regulation in the lac operon?
negative regulation… is lactose present or not? Is yes, make enzymes!
Describe the process of negative regulation in the lac operon when lactose is unavailable (glucose available)?
1 - lacl codes for the repressor protein.
2 - repressor protein binds to LacO, blocking RNA polymerase from transcription
Describe the process of negative regulation in the lac operon when lactose is available (glucose unavailable)?
1 - lacl codes for the repressor protein.
2- allolactose is an inducer and binds to the repressor protein, blocking it from binding to LacO.
3 - RNA polymerase carries out transcription
What is the purpose of positive regulation in the lac operon?
positive regulation… is GLUCOSE present or not? if Yes, use it as a better energy source!
Describe catabolic repression in lac operon?
The lac operon will use all of it’s glucose until it’s gone (repressing catabolism of lactose), experiences a short lag time, then begins to use lactose
Describe what happens at the CAP binding site on a lac operon?
CAP must bind to cAMP in order to increase the rate of transcription
When these two enzymes bind to CAP the levels of transcription are optimal
Is the CAP binding site a form of positive or negative regulation?
positive regulation - need a binding of something to allow transcription
