Bacterial Gene regulation Flashcards
what are the 3 qualities of an operon?
- gene promoter of variable strength; 2. mutliple genes (ORFs) of related function (2-20); 3. additional control mechs
how is regulation accomplished through attentuators?
sense the conditions to know if an enzyme is needed or not; as in, if there is enough of a certain nutrient, e.g. amino acid, transcription for the enzyme that synthesizes that aa will stopped
strong promoter=lots of RNA pol being bound, lots of mRNA produced
ya
how does a generic attenuator work?
case 1: enough aa around (being carried by tRNA)–> ribosome can work efficiently, quickly, tRNA comes with aa-X fast enough; ribosome is translating region 1–>therefore, regions 2 and 3 pair the stem-loops terminates transcription at the poly U-site
case 2: not enough tRNA carrying aa-X–>ribosome stalls at poly-X region; regions 1 and 2 form stable interaction and region 3 stays ss; RNA pol not terminated and copies full mRNA
what are riboswitches?
RNA-sensors; RNA seqs which will undergo a conformational change in response to a change in condition–condition, presence/absence of a target compound, etc; the change in conf can prevent or allow binding of Rho to terminate transcription prematurely, prevent/allow 16s rrna to bind to SD site; produces a ribozyme that will destroy itself if not needed
what is the lac I gene?
a repressor; it’s a weak sigma 70 promoter–>leads to low levels of mRNA and protein in the cell
how does the lac repressor interact with the DNA (Lac gene)?
a dimer of helix-turn-helix proteins will bind the DNA while each monomer binds the seq 5’-AATTGT-3’; tetramer binds two closely located “operator” regions;
what is escape expression?
something destabilizes the repressor (e.g. allolactose) and causes it to let go of DNA–>now DNA can be transcribed
how does catabolite repression work in the lac operon
Adenylate cyclase responds to glucose levels–> lots of glu, low activity, low cAMP; low glu, high activity, lots of cAMP–>cAMP binds to catabolite activator protein (CAP, a transcriptional activator); also recruit RNApol for extra effect
what is fourU?
RNA-thermometer from Salmonella–>located at the 5’ UTR of the mRNA for the Hsp AgsA; this Hsp prevents aggregation of of protein at higher temps (while infecting a mammalian host)
