Wright 7 - Four Regulatory Systems for Control of Prokaryotic Operons Flashcards
How did Jacob and Monod determine the regulatory mechanism of the lactose operon before the advent of gene cloning and DNA sequencing?
- They used mutants of the lac operon and its regulatory gene, lacI
- Construction of partial diploids (or meridiploids) with mutations in the lactose operon and its regulatory gene, lacI.
Where does the repressor protein (coded by the regulatory gene) bind to in the lactose operon? (eg. what part)
The operator
What is the phenotype of an E. coli strain carrying a mutation in the lacI gene (lacI-)?
The mutant repressor cannot bind to the operator, causing an abundance of constitutive beta-galactosidase, permease and transacetylase
Eg. constitutive synthesis, which is synthesis of a protein or an enzyme at a constant rate regardless of physiological demand or the concentration of a substrate.
What is the phenotype of a partial diploid where a string of E. coli with a mutation in ONE copy of the lacI regulatory gene?
There is no transcription of mRNA from the lac operon. Although one lacI repressor protein is mutant (and therefore inactive, suggesting constitutive synthesis) the other one is not a mutant and can repress transcription at both chromosomes.
What is a constitutive phenotype?
Where synthesis of a protein or an enzyme at a constant rate regardless of physiological demand or the concentration of a substrate.
It is where there is no regulation at the lac operon.
What is a non-inducible phenotype?
Where environmental conditions don’t induce a change in gene expression.
It is where differing levels of lactose can’t influence repressor gene activity, but repressor gene activity is still present. Ie, when there is a mutation in the lacZ gene (mutant beta-galactosidase).
What is an inducible phenotype?
A normal phenotype where environment can effect gene expression.
It is where high levels of lactose in medium causes greater expression of geta-galactosidase with no repression from allolactose allosterically binding to repressor protein.
How is the tryptophan operon (trp operon) regulated? What type of regulation is this?
- By the amino acid tryptophan
- It binds to a repressor protein, which then becomes active and binds to the operator, stopping RNA transcription.
This is repressible regulation. It stands in contrast to lactose’s inducible regulation
What is the inducer for the lac operon?
Allolactose, it binds to the repressor?
What is the represor and corepressor in tryptophan operon?
Repressor: Protein from regulatory gene
corepressor: tryptophan
What happens to tryptophan synthesis when tryptophan is present?
Tryptophan acts as a corepressor, which makes the repressor active and causes a stop in tryptophan trascription and therefore tryptophan synthesis.
In inducible operons what is the effector molecule?
The substrate
Eg. allolactose as inducer for beta-galactosidase and permease
In repressible operons what is the effector molecule?
The end-product
Eg. tryptophan as corepressor
How is the arabinose operon regulated?
By an inducible operon under positive control by an activator.
- The inactive operator binds to arabinose, this allows transcription to turn on.
What is a repressible operon under positive control like?
- An activator becomes inactive when it binds to an effector molecule
This is rare
