Final
Quiz yourself by thinking what should be in
each of the black spaces below before clicking
on it to display the answer.
Help!
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| Structure of the lac repressor | tetramer (dimer of dimers)
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| the lac repressor binds | LacO
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| how the lac operon moves along DNA | diffusion
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| Repressor does not block polymerase binding. Rather, | it inhibits open complex formation and elongation
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| Two mutations that allow constitutive lac expression to occur | lacI or Oc mutation
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| trans mutation: lac expression | lacI (repressor protein)
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| cis mutation: lac operon | mutation in the operator sequence
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| lactose & no glucose | expression of lac operon
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| lactose & glucose | no expression of lac operon
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| Class I CAP-dependent promoter | only require CAP-cAMP; binding site does not overlap promoter
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| Class II CAP-dependent promoter | Only require CAP-cAMP; binding site replaces -35 of promoter
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| Class III CAP-dependent promoter | Require multiple activators
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| When glucose levels are low, cAMP binds to a protein known as | Catabolite gene Activator Protein (CAP)
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| CAP is a homodimer of 210 aa subunits that has binding sites for | cAMP and DNA
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| When glucose levels are low (cAMP high), CAP-cAMP complex binds near | lac promoter
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| binding of CAP-cAMP complex near promoter does what? | stimulates transcription of lactose metabolizing genes
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| CAP can not bind DNA in absence of cAMP | cAMP thus allosterically regulates CAP
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| CAP responds to | glucose
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| Lac repressor responds to | lactose
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| 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
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| Glucose mediated catabolite repression is facilitated by | cAMP
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| CAP stimulates promoter recognition of | RNAP
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| In absence of lac repressor, expression is still | low
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| 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
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| AraC absent | araC transcribed + araBAD at basal level
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| cAMP and L-arabinose are low | AraC represses araBAD transcription
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| cAMP and L-arabinose abundant | araBAD transcription activated
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| trp operon | convert chorismate to tryptophan
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| trp operon modes of regulation | repression and attenuation
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| When this protein's levels are high, trp binds to it | L-tryptophan
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| trp regulation is feedback inhibition, aka | negative feedback loop
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| Attenuator is an RNA structure located within | 5' leader of nascent transcript
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| TrpR acts as a dimer, binds tryptophan, which induces a conformational change that allows | the protein to bind the operator
sequence
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