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Operons
Final
| Question | Answer |
|---|---|
| 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
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