Gene Expression - Lecture 2 Flashcards
When are genes for lactose transcribed?
when lactose is present and glucose is absent
Where is the lac operon located?
between purE and proA gene
What genes does the lac operon consist of?
lac repressor (I) gene, promotor (P), operator (O), and 3 structure Z,Y,A
What does the Y gene of lac operon control?
lactose transport
What does the Z gene of lac operon transport?
cleave lactose to glucose and galatose and some converts lactose to allolactose
Why can’t transcription occur when the repressor is bound to the operator?
the operator overlaps the initiation site, so when the repressor binds to the operator RNA polymerase cannot reach the initiation site and start transcription
What happens when the lac operon is OFF?
the inducer (allolactose) is absent, the lac repressor binds to the operator and prevents transcription
What happens when the lac operon is ON?
the inducer (allolactose) is present, lac repressor binds to inducer so it is unable to bind to operator and transcription occurs
What are Lacl superrespressors?
the lacl repressor is always bound to the operator always preventing transcription despite the presence and absence of lactose
What is laclP-?
prevents RNA polymerase from binding to promotor and stops transcription
How is lac operon effected by low levels of glucose?
cAMP levels are then high so cAMP binds to CAP and that complex binds to special region in lac promoter and transcription occurs
How is lac operon effected by high levels of glucose?
cAMP levels are then low so cAMP does not bind to CAP so transcription of lactose cannot occur because the cAMP/CAP does not exist to bind to lacl promoter
What is a negative inducible operon?
when an inducer is added to a repressor which causes the repressor not to bind the DNA strand so transcription occurs
What kind of control does cAMP induce on lac operon?
positive control
