regulation of transCription

all cells have all DNA- how is only some expressed? (DNA has large segments that code, and that regulate expression)

how is transCription regulated?

• low transCription: when RNA poly binds to the promoter

  • + activators

  • - repressors

key spots in DNA that relate to regulation

• promoter: where RNA poly binds

• operator: where repressor binds

lactose enzyme genes and what their proteins do:

• lacZ → breaks lactose into glucose + galactose

• lacY → transports lactose into cell

• lacA → detox

how lactose transCription is lowered in proks:

if no lactose enzyme → repressor on op (C block)

if lactose is there: allolactose binds to rep- op is off & transCription can happen

• Lactose present → allolactose binds repressor (can’t bind to op) → transcription allowed

how glucose level influences level of lactose transCription

if glucose is high, not much cAMP- CAP activator (+) pro can’t bind to promoter- low transcription

if glucose low, lots of cAMP, CAP activator (+) pro binds to promoter- MORE TRANSCIPTION

• Max transcription = lactose present + glucose low

what does the TrP operon do? (makes tryptophan AA)- it’s a corepressor

Regulation:

• Low tryptophan → operon ON → genes transcribed

• key for repressor: High tryptophan → tryptophan AA binds to repressor (-) → activates it (key)→ repressor (-) binds to operator (no transCription)

what is lac operon default?

• c block on op (repressor on operator)