Download trp

Control Mechanisms
{
Miss Richardson
SBI4U

There are four levels of control of gene
expression:
1.
-Regulates which genes are
Transcriptional transcribed
-Controls rate of transcription
2. Post-Modification of mRNA
transcriptional -Introns removed and exons
spliced together
Control of Gene
Expression

There are four levels of control of gene
expression:
3. Translational -Controls rate of translation
-Controls rate of mRNA activation
and destruction
4. Posttranslational
-Controls rate at which a protein
becomes active and the time it
remains functional
Control of Gene
Expression
E. coli uses β-galactosidase to break down
lactose in order to grow.
 The 3 genes for β-galactosidase are part
of the lac operon.

The lac Operon

When lactose is absent:
 LacI repressor protein binds to the
operator and partially blocks the
promoter.
 Prevents transcription of the lac
operon genes
The lac Operon

With sufficient lactose:
 Binds to the LacI repressor protein.
 LacI changes its shape, allowing
transcription of the lac operon genes
The lac Operon
E. coli uses tryptophan for the production
of protein.
 The trp operon consists of 5 genes that
code for 3 enzymes needed to synthesize
tryptophan.

The trp Operon

When tryptophan is absent:
The shape of the trp repressor
protein changes.
 No longer binds to the trp operator.
 RNA polymerase transcribes trp
operon genes.

The trp Operon

With sufficient tryptophan:
Binds to the trp repressor protein,
causing a change in shape.
 trp repressor-tryptophan complex
binds to the operator.
 Prevents transcription of the trp
operon genes.

The trp Operon
lac Operon
 Transcription induced when high levels
of lactose present.
 Effector = level of lactose
trp Operon
 Transcription repressed when high levels
of tryptophan present.
 Effector = level of tryptophan
Summary