RNA Synthesis: Transcription Flashcards
What is RNA a key component in?
- Synthesis of proteins
- Splicing of genes
- Transfer of genetic information from nucleus to cytoplasm
What is the most abundant RNA in cells?
rRNA
What are the similarities in DNA and RNA synthesis?
- Need a template
- 5’ to 3’ polarity
- Proceeds in 3 phases
What are the differences between DNA and RNA synthesis?
- RNA Pol needs no primer
- Only genes in DNA gets transcribed
- RNA is complimentary to one DNA strand
Where is Transcription initiated and ended?
Initiated at promoters and ends at terminators
What binding site do promoters recognise?
Sigma 70
No proofreading activity but can pause
What binding site is recognised by the RNA Pol sigma subunit?
TATA box
What are the steps for Initiation and Elongation in Transcription?
1. Polymerase binds promoter
* Close complex
* DNA still inact
2. Transcription bubble forms
* Open complex
* DNA unwinds over 12-15 bases
3. Transcription starts
* Promoter clearance
* Elongation
* Sigma dissociates
* Proceeds to termination
What are the TWO ways in which transcription is terminated?
- Rho-independent transcription
- Rho-dependent transcription
What happens in Rho-Independent termination?
- Terminator sequence (pallindrome) causes hairpin in RNA and disrupts the RNA-DNA hybrid
- Conserved polyA sequence in DNA generates polyA=U at end of RNA which is unstable so dissociates
What happens in Rho-Dependent termination?
- Polymerase pauses at termination site
- Rho helicase binds to RNA
- Associates with Rho utilisation element (Rut)
- Faciltates dissociation of RNA
What are the THREE polymerases used in Eukaryotic transcription and their roles?
- Pol I: synthesis of pre-ribosomal RNA
- Pol II: synthesis of mRNAs and ncRNA
- Pol III: synthesis of tRNAs and ncRNAs
Where is the TATA box located in many Pol II promoters?
-30
How many subunits does RNA Pol II have?
12
What are the phases of Transcription?
- Assembly
- Initiation
- Elongation
- Termination
Which polymerase do Transcripton Factors (TFs) associate with?
Pol II at DNA
What are the proteins required for Elongation?
- ELL
- PTFB
- SII (TFIIs)
- Elongin
Act to ensure transcription proceeds and to prevent pausing by the Pol II TFIIH complex
What are the steps for Eukaryotic Pol II Transcription?
- Assembly of Pol II complex subunits at promoter
- Initiation: TFIIH kinase phophorylates Pol II on C terminal domain (CTD)
- Elongation factors assist Pol II
- Termination factors stop transcription
Which antibiotics intercalates in DNA and inhibits polymerase?
Actinomycin D & Acridine
Which antibiotic binds to the beta subunit of bacterial polymerases?
Rifamycin
Which antibiotic from Amanita phalloides inhibits RNA Pol II?
α-amantin
