Prokaryote regulation of gene expression Flashcards
Describe inducible, repressible, and constitutive
inducible - turned on when a certain molecule is present
repressible - turned off when a certain molecule is present
constitutive - always turned on
Describe the lac operon
Lactose is the inducer, three structural genes including lacZ, lacY, and lacA
Allosteric lacI repressor is also present that is removed from operator when lactose is present
What is an operon?
A group of genes that are clustered together and regulated/expressed together
Describe the Oc and Is mutants
Oc- operator can’t bind repressor, constitutive expression
Is- super repressor always bound to operator, no expression
What is the function of CAP?
Represses lac operon expresión when glucose is present
When glucose is absent and lactose is present, CAP binds to the CAP binding site and causes positive control of the lac operon
cAMP required for CAP binding,
Adenyl Cyclase, which produces cAMP, is repressed by glucose
What are the functions of lacY, lacZ, and lacA
lacZ encodes B-galactosidase, which converts lactose to glucose and galactose,
lacY specifies the primary structure of permease, which allows lactose to enter the cell.
lacA codes for transacetylase which may be involved in removal of toxic byproducts of lactose digestion
What are the features of the trp operon?
Repressible by tryptophan, which functions as a corepressor to the repressor.
Involves a leader sequence that be transcribed even when the operon is repressed
What is attenuation
Mechanism by which the rest of the trp operon isn’t transcribed after the leader sequence is.
When tryptophan is absent, transcription isn’t terminated in leader region.
What is the mechanism of attenuation?
When tryptophan is absent, an antiterminator hairpin forms to allow transcription to proceed
When tryptophan is present, a terminator hairpin forms to prevent further transcription.
