Lecture 39. The lac Operon Flashcards
What is an operon?
A group of genes under control of the same promotor
Are operons more common in eukaryotes or prokaryotes?
Prokaryotes
Are all genes constitutively expressed?
No as making RNA and protein is energy costly
What does diauxic growth mean?
Two growth phases
What two carbon sources are used by E. coli?
Glucose and lactose (in that order)
Are the carbon sources used consecutively or simultaneously?
Consecutively
What does the lacY gene encode?
β-galactoside-permease
What does the lacZ gene encode?
β-galactosidase
What does the lacA gene encode?
Galactoside acetyl-transferase
What does galactoside acetyl-transferase do?
Transfers an acetyl group to galactosides LacY
and glucosides - function unknown
Is the lac operon usually turned on or off?
Off
When the operator is bound by a repressor, is the operon turned on or off?
Off
What is the inducer of the lac operon?
Allolactose
What is an inducer?
Molecule that turns gene on and disables the repressor
What happens in the lac operon when lactose is present?
RNA Polymerase binds the promoter, and make LacZ, LacY, LacA mRNA
Why are genes not induced from the start in the lac operon?
Glucose suppresses activation
What enhances transcription in the lac operon and how does it function?
Catabolite Activator Protein (CAP) interacts with cAMP and binds to DNA which enhances transcription by ~50 times
What inhibits cAMP production and how does this molecule inhibit this production?
Glucose inhibits adenylate cyclase which makes cAMP
What is one of the most useful promotors in biotechnology?
The lac promotor
