Operons Flashcards
what do prokaryotic operons contain
operators - segment of DNA that regulates activity of the structural genes of the operon
what happens if operator is bound by a repressor molecule
RNA pol is blocked and does not produce mRNA
what does an inducer molecule do
it binds to repressor hence changing its shape and now can no longer bind to the operator
transcription proceeds
lac operon codes for what proteins
lacZ, lacY, lacA
what does lacZ code for
beta galactosidase - hydrolyzes lactose to galactose and glucose
what does lacY code for
permease - facilitates movement of lactose into the cell
what does lacA cod for
thiogalactoside transacetylase - acetylases lactose
when are the proteins of lac operons maximally produced
when lactose is available to the cell but glucose is not
what codes for the repressor protein
lacI gene
what happens to the lac operon when only glucose is present
lac operon is repressed
mechanism that the lac operon uses to repress itself
repressor binding protein binds to the operator site downstream of promoter region via a helix-turn-helix motif
lac operon being repressed is an example of what type of regulation
negative regulation
when is the lac operon maximally expressed
when only lactose is availabe
when only lactose present what is used to stop the repressor protein
allolactose - isomer of lactose
what does allolactose do
it binds to repressor protein and changes it conformation hence stopping it from binding the operon
what enzyme is active when glucose not present but lactose is
adenylyl cyclase - cAMP is made and binds to CAP protein
what does the cAMP-CAP trans acting complex do
binds to CAP site making RNA pol more efficiently initiate transcription at promoter sie
cAMP-CAP doing it job is an example of what type of regulation
positive regulation
what happens with the mRNA produced after initiation of the lac peron
it produces the three proteins - lacZ, lacA, lacY
what happens with the transcription of lac operon when both glucose and lactose available
it is negligible because adenylyl cyclase is inhibited by the glucose
what role does the repressor protein play when both glucose and lactose are present
it could remain unbound but no lac operon would be transcribed because glucose is inhibiting the adenylyl cyclase from forming he cAMP-CAP trans acting complex
