Prokaryotic and Eukaryotic Transcription Flashcards
(24 cards)
How are bacterial genomes organised?
Single circular chromosome + extra DNA in plasmids (much smaller than the main chromosome)
How are eukaryotic genomes organised?
Mutliple linear chromosomes + extra DNA in mitochondria
What is an operon?
A cluster of genes transcribed together under a single promoter, forming a polycistronic transcript that is translated into multiple proteins
What features make eukaryotic genomes more complex?
Protein-coding genes (with introns)
Non-coding RNA genes
Origins of replication
Repeats
Specialised structures (centromeres and telomeres)
What is RNA Polymerase (RNA-Pol)?
A large mutli-protein complex that reads DNA and catalyses mRNA synthesis
What is the transcription bubble?
RNA-Pol unwids the DNA helix, moves 3’ to 5’ along the template strand, and rewinds DNA after transcribing
What are the three basic stages of transcription?
Initiation - RNA-Pol binds to the promoter, recogniseng the gene to be transcribed
Elongation - DNA is metlted, and RNA-Pol moves along the template strand, extending the RNA chain at the 3’ end
Termination - Transcription stops when the RNA strand is complete
What are the main subunits of bacterial RNA Polymerase?
α subunits - Scaffold for core enzyme assemply
β and β’ subunits - Catalytic domains froming
- Active site
- DNA entry channel
- Substrate ribonucleotide entry channel
σ factor - Promoter recognition and specificity
What does the sigma factor do?
Enhances RNA-Pol promoter binding (1000x higher affinity)
Determines which genes are transcribed
Is released after mRNA reaches 10 bases (promoter escape)
How do different sigma factors function?
σ70 - General housekeeping genes
σF - Flagella/movement genes
σ32 - Heat shock response genes
What does RNA Polymerase II do?
Synthesises mRNA in eukaryotic cells
Why can’t eukaryotic RNA-Pol II initiate transcription alone?
It requires general trasncription factors (GTFs) to bind DNA
What are the key GTFs in eukaryotic transcription?
TFIIA
TFIIB
TFIID
TFIIE
TFIIH
What are the functions of the GTFs in eukaryotic transcription?
Promoter recognition
RNA-Pol recruitment
DNA unwinding
Transcription start site recognition
What are teh steps in eularyotic transcription initiation?
1 - TFIID binds the promoter (TATA-box) - bends DNA by 80 degress
2 - TFIIB binds TBP - Forms TBP-TFIIB complex
3 - TFIIB bridges RNA-Pol II via TFIIF - Recruits Pol II
4 - TFIIE and TFIIH melt DNA - TFIIH has ATPase, helicase, kinase activities
What is the CTD domain of RNA Pol II?
The Carboxy-terminal domain of Rpb1, which is phosphorylated dueing transcription
What is the role of CTD phosphorylation?
Regulates:
Initiation, elongation, termination
RNA processing (5’ capping)
What are basal promoters?
Short sequences (100 bp) that bind transcription factors for initation
What are enhancers and silencers?
Enhancers - DNA elements binding activator proteins, looping DNA to interact with RNA-Pol II
Silencers - DNA sites binding repressors, blocking transcription
What is teh intiatior (Inr)?
Minimal core promoter sequence (-2 to +4 bp) that enables Pol II transcription
What is trh TATA-box?
A TATA-rich sequence (25 bo upstream) of the transcription start site
What is teh Downstream Promotre Element (DPE)?
Found at +30 p, requred for transcription in TATA-less promoters
What are distal control regions?
Enhancers located >100-200 bp from the gene, affecting transcription by looping DNA
How do enhancers function?
Bring activator proteins to the promoter, aided by Mediator complex, which recruits RNA-Pol II
