LAC OPERON REVISION QUESTIONS WITH
100% CORRECT ANSWERS!!
Why do bacteria not need to always express their entire complement of genes?
Their environment is ever changing
Jacob and Monod showed that what?
a) E coli can regulate expression of its genes
b) Genes for a metabolic pathway (structural genes) are grouped on a chromosome and
transcribed at the same time
What model did Jacob and Monod propose?
What did it explain?
Operon Model
Gene regulation in prokaryotes
Operons contain what four elements?
PROG:
1. Promoter
2. Regulator gene
3. Operator
4. Genes (Structural)
1. Regulator gene
Located outside the operon
Codes for DNA-binding protein that acts as a repressor
Repressor
Coded for by regulator gene
Controls whether the operon is active or not
, 2. Promoter
Short DNA sequence
RNA polymerase attaches here (to begin transcription)
Signals two things: Start of the Operon and Location where transcription begins
3. Operator On-Off Switch
Short bit of DNA where an Active repressor binds
When active repressor binds here, RNA polymerase can't attach to the promoter, so transcription
can't happen
This is how the operator controls transcription of structural genes
4. Structural genes
Code for enzymes/proteins of operon's metabolic pathway
They're transcribed as one unit
PROG image (for Lac Operon)
Lac operon taking in Lactose molecule
Lac Operon
Repressor then leaves and changes shape. This makes room for RNA polymerase to now
attach to promoter and move down the DNA sequence to make mRNA that codes for the
proteins (to break down lactose)
Note: The Promoter, Operator and Genes (top) are all DNA.
But the Repressor is different - it's a protein that came from a different part of the DNA
RNA polymerase attaches to Promoter when repressor is out of the way
Lac Operon
Operator in Off Position when no lactose present
The repressor is opposite - it's Activated here (physically blocking RNA polymerase).
If lactose had been present and is now gone, the repressor changes back to this shape and
reattaches to the operator.
100% CORRECT ANSWERS!!
Why do bacteria not need to always express their entire complement of genes?
Their environment is ever changing
Jacob and Monod showed that what?
a) E coli can regulate expression of its genes
b) Genes for a metabolic pathway (structural genes) are grouped on a chromosome and
transcribed at the same time
What model did Jacob and Monod propose?
What did it explain?
Operon Model
Gene regulation in prokaryotes
Operons contain what four elements?
PROG:
1. Promoter
2. Regulator gene
3. Operator
4. Genes (Structural)
1. Regulator gene
Located outside the operon
Codes for DNA-binding protein that acts as a repressor
Repressor
Coded for by regulator gene
Controls whether the operon is active or not
, 2. Promoter
Short DNA sequence
RNA polymerase attaches here (to begin transcription)
Signals two things: Start of the Operon and Location where transcription begins
3. Operator On-Off Switch
Short bit of DNA where an Active repressor binds
When active repressor binds here, RNA polymerase can't attach to the promoter, so transcription
can't happen
This is how the operator controls transcription of structural genes
4. Structural genes
Code for enzymes/proteins of operon's metabolic pathway
They're transcribed as one unit
PROG image (for Lac Operon)
Lac operon taking in Lactose molecule
Lac Operon
Repressor then leaves and changes shape. This makes room for RNA polymerase to now
attach to promoter and move down the DNA sequence to make mRNA that codes for the
proteins (to break down lactose)
Note: The Promoter, Operator and Genes (top) are all DNA.
But the Repressor is different - it's a protein that came from a different part of the DNA
RNA polymerase attaches to Promoter when repressor is out of the way
Lac Operon
Operator in Off Position when no lactose present
The repressor is opposite - it's Activated here (physically blocking RNA polymerase).
If lactose had been present and is now gone, the repressor changes back to this shape and
reattaches to the operator.
