BC 16 Transcription Flashcards
Similarities to Replication
phosphodiester bonds linking nucleic acids
5-3
new strand complementary to tamplate strand
Differences
ribonucleotides
Uracil instead of thymine
RNA product gets displaced
RNA pol does not need primer
Only for specific genes
Many copies
Types of RNA
mRNA: coding sequence
tRNA: protien synthesis
rRNA: ribo RNA, makes ribos
snRNA: mRNA splicing
RNA pol
Prok: single RNA pol
Euk
RNA Pol 1: transcribe three major rRNA (5.8s 18s 28s)
RNA pol II mRNA
RNA pol III: tRNA (some rRNA and snRNA)
Transcribed region
5’ UTR (untranslated region)
AUG, protien coding region
3’ UTR,
STOP
Prokaryotic transcription
RNA pol Six subunits -catalyzes RNA synthesis but cannot initiate elong. 2 alpha 1B 1B' 1 omega
-facelitates polymerase binding to DNA at -35 and -10 promoter elements
Sigma subunit
1 sigma
Prokaryotic promoter
from +1 back to -35. Includes -10.
Binds RNA pol
- 10 = AT rich- easier to unwind and bend to initiate transcription:
- consesnsus sequence:conserved across genes. Polymerase will always recognize the appropriate binding site
Prokaryotic transcription
- Initiation: RNA pol holoenzyme binds to -10 and -35 using sigma subunit (below) (DNA not unwound) (promoter melting)
- open promoter complex- Unwinding of DNA around the initiation site. (does not need helicase)
- RNA pol makes 10 nucleotides short transcript, the sigma subunit is then released.
- elongation begins
- only about 15 bp long bubble, RNA pol unwinds and religates - TERMINATION: signal sequence DNARNA is released
- Rho independant: intrinsic, spontaneous, no protein needed. Hairpin disrupts RNA pol releases it
- Rho dependent term: rho binds to rho recognition site, when RNA pol is paused at term site, ATP dependant helicase activity of Rho separates RNA DNA hybrid helix. releases RNA
WHY have two??
Rifampicin
antibiotic interfere with RNA synthesis
usd to treat TB, wims and Weings tumors, test. cancer, carcomas, (dactinomyycin)
-action: inhibits transcription by binding to B subusing of prok polymerase. Prevents growth
Eukarytotic Transcription differences
THREE RNA pols
numerous IF’s and GTF (general transcription factors) to initiate transcription
Eukaryotic Trancription Initiation complex
DRAW
- TFIID Binds to the AT rich promoter (TATA Box)
- multisubunit compled of TFIID contains Tata binding protiens (TBP)(allows TFIID to recognize tata) - TFIIA assists with TFIID binding to tata
- TFII B orients the polymerase
- RNA pol II bound to GTF at teh promoter -carboxy terminal domatin (CTD) or RNApol II held in place by GTF’s
- TFII E intereactes with promoter bound RNA pol II
- TFII E recruits and regulates TFIIH
- binding of TFIIH completes the pre initiation complex (PIC)
Euk Transcription Initiation
- TFIIH is a multisubunit protein that has two activities
- helicase: ATPase unwinds dna at initiation site
- kinase: phosphorylates C terminal domain of RNA pol II
- phosphorylated CTD no longer binds to GTF’s and releases GTF’s
- elongation begins wit just RNA pol II
terminated at stop codon
5’ Cap
Occurs first, addition provides direction of where go to and stabilizes
-7-methylguanosine (methylated guanasine molecule at position 7 of purine ring) as soon as mRNA synthesis begins. first and second nucleotides can be methylated too
protects from DNA by stabilization
positions mRNA for initiation of translation
3’ pA addition
Occurs after 5’ cap. pA added for stabilization
Splicing of Introns
Last post transcription mod
not yet spliced referered to as primary transcript or pre mRNA
15% inherited human disease splicing errors
GU- 5” splicing
A: branch point of lariat formation
AG: site of splicing at 3” end.
- cleavage of 5” end
- folding for intron to a lariat stucture at branch point
- cleave at 3’ end
- assembly of neighboring exons
- lariat degraded in nucleus
snRNA: splicosomes, five types of RNA combined with over 200 snRNP.
Splice AND ligate exons
