Week 9: Transcription And Regulatory Networks Flashcards
What is the central dogma of molecular biology?
DNA → RNA → Protein
What enzyme carries out transcription?
RNA polymerase
What are the main subunits of RNA polymerase in E. coli?
- β, β’-subunits
- α-subunits
- ω-subunit
- σ-factor
What role do magnesium ions play in nucleic acid processing?
They are ubiquitous in enzymes that process nucleic acids.
How does RNA polymerase initially move to the promoter of a gene?
By diffusion (three-dimensional random walk)
What happens when RNA polymerase encounters DNA?
It binds unspecifically and slides along the DNA, transitioning to a one-dimensional random walk.
What triggers the start of RNA synthesis?
Consensus sequences such as TCTTGACA, AGAACTGT, TATAAT, ATATTA.
How does the strength of a promoter affect transcription?
The closer the promoter sequence resembles the consensus sequence, the stronger the interaction with RNA polymerase.
What are the two basic forms of transcriptional regulation in bacteria?
- Strength of the promoter
- Sigma factor involved
What is formed when a promoter is bound by RNA polymerase?
An open complex
What is the typical RNA synthesis rate by RNA polymerase?
Approximately 30 – 50 nt/s
What are the two main mechanisms for termination of transcription?
- GC hairpin formation
- Rho (ρ) factor interaction
What is the accuracy of transcription in vivo?
Approximately 1 × 10–5
What is the half-life of mRNA in bacteria?
Approximately 7 minutes
What happens during head-on collisions between replication forks and transcription complexes?
They create extremely stable complexes with a long half-life.
What is the role of activator proteins in transcription?
They help recruit RNA polymerase complexes.
What is Class I activation in transcription?
Binding of activator proteins near or at the promoter.
What is the role of repressor proteins in transcription?
They prevent binding of RNA polymerase complexes.
What is the significance of the lactose operon in gene expression regulation?
It is regulated on several levels including the binding of repressor proteins.
What happens when lactose is available to the cell?
Lactose is isomerised into allolactose, which binds to the repressor and changes its shape.
What is required for strong transcription of the lac operon?
Binding of CAP protein (catabolite activator protein).
What does cAMP indicate in the context of glucose levels?
cAMP levels are high when glucose is absent.
What is quorum sensing?
A regulatory network in bacteria such as Vibrio fischeri.
What is the function of LuxI in Vibrio fischeri?
It produces the auto-inducer AHL (acetyl-homoserine lactone).