Transcription Flashcards
Gene
DNA sequence that’s transcribed
- might not code for protein
- cont controlling transcription
RNA composition
Large % rRNA and small mRNA (rapid degradation)
RNA P characteristics
- Catalyses DNA-directed RNA synthesis/transcription
2. Oligomeric protein with 4 different types of sub-units
RNA P sub-unit composition
5 make core enzyme
- large beta and beta’ subunits = active site
- > beta = polymerase, beta’ = binding
- alpha = scaffold and assembly
Theta sub units
Transcription initiaion
- > bind to core enzymes in w subunit
- > theta 70 in E.coli
Outline the chain elongation reaction
- Growing RNA chain is base-paired to DNA template
- Incoming ribontriphosphates with correct H-bond
- Nucleotidyl group transfer reaction
- ppd linkage + release of pyrophosphate
What’s the 5’->3’ reaction equation for chain elongation
RNAn-OH + NTP -> RNA n+1-OH + PPi
How is chain elongation thermodynamically favourable?
Delta G decreases because high NTP: RNA
-> assisted by pyrophosphate hydrolysis
Which linkages are expended for chain elongation?
2 phosphoanhydride linkages/ nucloetides added to chain
What’s the error rate of chain elongation in prokaryotes?
10^-6 because no 3’->5’ exonuclease
Growing RNA strand only interacts with template over ___________ forming a ________ product
Short distance, single-stranded
Transcripts of _____ length are ______ along genes because ______
Increasing, arrayed, many RNAP transcribe at same time
Which two consensus sequences are used in prokaryotes with theta 70 promoters?
TATA -10 bp -> melts within active site
Recognition - 35 bp
How is the promoter sequence found?
1D diffusion of RNA P along DNA molecule where enzymes bound non-specifically -> scan 2000 bp for promo sequence
Which is the slowest step of initiation events?
RPC -> RPO ( conformational change of RNA and promoter complex)
Outline RPO to promotor clearance
- Temp. strand at polymerisation site
- Ppd link between 2 ribonucleoside triphosphates
- H bond with +1 and +2 nucleotides of template
- Additional nucleotides added to dinucleotide
- At 10, RNA P -> transition to elongation away from promoter -> release of theta sub-unit with help of accessory proteins
Where does transcription termination usually occur?
Near pause site, dyad symmetry, palindromic e.g. G-C rich region (+difficult to melt)
Outline hair pin formation
Hairpin formation at transcription destabilises RNA-DNA off part of newly transcribed RNA
- > NusA stabilises hairpin
- > wealky bound to A/V -> easy disruption
Rho-independent
Destabilising of structure -> GC bases strong => 8 AT bp
Rho
Hexameric ringed protein with potent ATPase activity and affinity for ssRNA
-> acts as RNA. DNA helicase
Rho-dependent
80 RNA nucleotides wrap around Rho at rut sites -> dissociate from transcription complex
When is ssRNA available?
Only when protein synthesis terminates as translating ribosomes interfere with rho -> minimises wasteful transcription
