Transcription In Eukaryotes Flashcards
RNA Polymerase 1 in Eukaryotes
Synthesis of: 5.8S rRNA 18S rRNA 28S rRNA (produced from cleavage of 45S pre rRNA
RNA Polymerase 2 in Eukaryotes
Synthesis of:
mRNA, miRNA, & most snRNA
RNA Polymerase 3 in Eukaryotes
Synthesis of:
tRNA
5S rRNA
1 type of SnRNA
Eukaryotic Primer Elements
- TATA (hotness) box
2. CAAT and GC Box
Eukaryotic Primer- TATA Box location, sequence, and binding
Located 20-30 bp upstream from start point
consists of 5’ TATAAA 3’
Binds to TATA Binding Protein (TBP) of TFIID (Transcription Factor IID) which represents first step in formation of transcription complex on promotor
Eukaryotic Primer- CAAT and GC Box Location and Binding
Located 40-200 bp upstream from start point
Bind to protein that control frequency of transcription
Steps of transcription
- Template binding and formation of Pre initiation complex
- Initiation
- Elongation
- Termination
Template binding and formation of pre initiation requirement
requires RNAP 2 and general transcription factors (GTF)
What happens in preinitiation?
TBP binds to TATA box
first step of transcription
binding of TBP to Tata box
TFIIH has
high helices activity
TFIIH brings
RNA Polymerase 2 to promotor
termination signal
AAUAA
Post transcriptional modification of mRNA in prokaryotes vs eukaryotes
prokaryotes: Once mRNA is synthesized, its immediately available for translation
eukaryote: Needs modification/Extensive processing
prokaryote: Mono or Polycistronic: codes for 1 ore more proteins
eukaryote: Monocistronic: codes for only one protein
mRNA is synthesized as a primary transcript known as
heterogenous (hnRNA)
Post transcriptional modification includes
capping
polyadenylation
splicing
mRNA editing
mRNA protein complex
newly synthesized mRNA binds with protein to form this which comes out of nucleus by nuclear pore
capping occurs at
5’ end of 7 methyl GTP
mechanism of capping
RNA triphosphatase hydrolyze terminal y phosphate of mRNA to form diphosphate.
Guanylyl transferase adds GMP to diphosphate to make DTP
Methlyation of GTP by SAM
importance of capping
protects 5’ end from exonuclease
important for initiation of translation by binding to cap binding protein (IF4)
Directs mRNA from nuclease to cytosol
polyadenylation definition and enzyme
addition of poly a tail at 3’ end by poly a polymerase
where does poly a polymerase bind to
poly A tail binding protein
importance of poly A tail
protect 3’ end from nuclease
increase 1/2 life of mRNA
increases efficiency of translation
splicing definition
precise cutting of introns and joining of exons
