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Operons

Final

QuestionAnswer
Structure of the lac repressor tetramer (dimer of dimers)
the lac repressor binds LacO
how the lac operon moves along DNA diffusion
Repressor does not block polymerase binding. Rather, it inhibits open complex formation and elongation
Two mutations that allow constitutive lac expression to occur lacI or Oc mutation
trans mutation: lac expression lacI (repressor protein)
cis mutation: lac operon mutation in the operator sequence
lactose & no glucose expression of lac operon
lactose & glucose no expression of lac operon
Class I CAP-dependent promoter only require CAP-cAMP; binding site does not overlap promoter
Class II CAP-dependent promoter Only require CAP-cAMP; binding site replaces -35 of promoter
Class III CAP-dependent promoter Require multiple activators
When glucose levels are low, cAMP binds to a protein known as Catabolite gene Activator Protein (CAP)
CAP is a homodimer of 210 aa subunits that has binding sites for cAMP and DNA
When glucose levels are low (cAMP high), CAP-cAMP complex binds near lac promoter
binding of CAP-cAMP complex near promoter does what? stimulates transcription of lactose metabolizing genes
CAP can not bind DNA in absence of cAMP cAMP thus allosterically regulates CAP
CAP responds to glucose
Lac repressor responds to lactose
restricts the expression of genes required for catabolism of arabinose, lactose, and other simple sugars in the presence of glucose, even when this secondary sugar are abundant Catabolite repression
Glucose mediated catabolite repression is facilitated by cAMP
CAP stimulates promoter recognition of RNAP
In absence of lac repressor, expression is still low
CAP-cAMP complex activates by two mechanisms: (i) direct interaction with RNAP (α subunit) and (ii) Conformational change - DNA bending (~90 o ) CAP interacts with the RNAP via its C-terminal domain
AraC absent araC transcribed + araBAD at basal level
cAMP and L-arabinose are low AraC represses araBAD transcription
cAMP and L-arabinose abundant araBAD transcription activated
trp operon convert chorismate to tryptophan
trp operon modes of regulation repression and attenuation
When this protein's levels are high, trp binds to it L-tryptophan
trp regulation is feedback inhibition, aka negative feedback loop
Attenuator is an RNA structure located within 5' leader of nascent transcript
TrpR acts as a dimer, binds tryptophan, which induces a conformational change that allows the protein to bind the operator sequence
Created by: ScarlettRose