August 7 2019 Regulation Gene Expression in Prokaryotes Flashcards
In Prokaryotes: What is a repressor? What does it do?
Regulatory proteins, involved in operon regulation, in prokaryotes that bind to operator sequences to prevent the binding of RNA polymerase to the promoter, which in turn is acting on the initiation of transcription.
If transcription does not occur, no proteins are produced.
compare derepression in the lac and trp operons
- Lactose binds to repressor, which no longer binds to DNA.
- In the absence of tryptophan the aporepressor cannot bind to the operator
Does attenuation require a stop codon during tryptophan starvation in E. coli? Why or why not?
No; under conditions of tryptophan starvation, the ribosome stalls at adjacent Trp codons in sequence 1, which prevents 1-2 stem loop and promotes 2-3 stem loop formation; no terminator, polymerase continues
In Prokaryotes: What is an inducer? What does it do?
Small molecule–either a nutrient or metabolite of the nutrient
Involved in operon regulation
Stimulates expression of the operon by binding to the repressor and changing its conformation so that the repressor can no longer bind to the operator
What is a corepressor? What does it do? What happens when a corepressor does its job?
Small molecule–either a nutrient or its metabolite
Involved in operon regulation
Binds to an inactive repressor protein, activating it
Repressor-corepressor complex then binds to the operator, preventing the binding of RNA polymerase and preventing gene transcription from occuring
What occurs when an inducer is not present at the operon of the gene?
The repressor is active, transcription is repressed, and the genes of the operon are not expressed.
What is a corepressor? What does it do? What happens when a corepressor does its job?
Small molecule–either a nutrient or its metabolite
Involved in operon regulation
Binds to an inactive repressor protein, activating it
Repressor-corepressor complex then binds to the operator, preventing the binding of RNA polymerase and gene transcription
Does attenuation require a stop codon during tryptophan starvation in E. coli? Why or why not?
No; under conditions of tryptophan starvation, the ribosome stalls at two Trp codons, which prevents 1-2 stem loop and promotes 2-3 stem loop formation
In trp operon regulation; when tryptophan is HIGH, the repressor is ___ and the operon is ___ (on/off).
In trp operon regulation; when tryptophan is HIGH, the repressor is ACTIVE and the operon is OFF.
What are some differences in the structure of the E. coli chromosomes and eukaryotic chromosomes?
Prokaryotes
DONT: have histones, a nuclear envelope or nucleosomes
DO: have polycistronic transcription units
When glucose is present; what happens to cAMP and CRP?
cAMP levels are decreased and CRP assumes inactive conformation (does not bind to the operon).
