Download Operon Comparison Chart

REVIEW OF OPERONS
OPERONS  controls gene expression in prokaryotes
REPRESSIBLE
- Operon is usually ON (can be
turned off)
- Repressor is made in the
INACTIVE form
- Ex. TRP OPERON
- Makes tryptophan
- When too much
tryptophan is made, it acts
as a corepressor (binds to
the repressor to activate
it), which turns the operon
OFF (so no more
tryptophan is made)
INDUCIBLE
- Operon is usually OFF (can be
turned on)
- Repressor is made in the ACTIVE
form
- Ex. LAC OPERON
- Breaks down lactose to
get ATP
- Only switched ON when
lactose (allolactose) is
present (it only needs to be
on if lactose is available to
be broken down!!)
- Allolactose is an inducer
- Dual Control (negative =
repressor; positive =
presence of glucose)
Parts of an Operon:
1. OPERATOR – on/off switch
2. PROMOTER – where RNA polymerase binds
3. Genes it controls
*** The REPRESSOR (protein – not DNA) is coded for by a regulatory gene
SUMMARY of Positive regulation in Lac Operon:
↑ Glucose = ↓ cAMP which means Lac operon on a LITTLE
↓ Glucose = ↑ cAMP which means ACTIVE CAP which means Lac operon on
a LOT