Transcription 2 Flashcards
(19 cards)
What are the three phases of transcription?
Initiation, Elongation and Termination
Initiation
Creates a open transcript complex. Transcription bubble is created during this step and the first ten nucleotides are polymerized together by RNA polymerase. Sigma factor is also released from RNA polymerase
Termination
Occurs by both factor dependent (needs protein) means and independent means.
Factor Dependent Termination
Relies on formation of a duplex sequence of base pairs ahead of a stretch of U’s. The duplex destabilizes the RNA-DNA-RNA polymerase complex. Kicks RNA polymerase off DNA.
What is rho?
It is the factor involved in factor dependent transcription termination in E. Coli.
What does rho do?
Binds to the 5’ end of RNA being made and climbs the RNA until ir reaches the polymerase. Once there, it destabilizes the duplex, favoring release of RNA polymerase.
Difference between eukaryotes and prokaryotes with transcription and translation?
Prokaryotes have no nucleus. Therefore translation starts oftentimes while a message is being transcribed. There is no significant modifications to mRNAs in prokaryotes. Whereas in eukaryotes, both are spatially separated. Transcription occurs in the nucleus, where translation occurs in the cytoplasm.
Eukaryotic mRNA modification?
It is capped at the 5’ end and polyadenylation at the 3’ end. There is editing and splicing that occurs in the middle of the strand.
How many RNA polymerases do Eukaryotes have?
3 - I, II, III - they differ in sensitivity to alpha-amanitin
RNA Polymerase I
Makes Large rRNA (low sensitivity)
RNA Polymerase II
makes mRNA (most sensitive)
RNA Polymerase III
makes tRNA and small rRNA (moderate sensitivity)
TATA Box
A sequence element that affects transcription of eukaryotic genes. (-30 to -100)
CAAT box and GC box
A sequence element that affects transcription of eukaryotic genes (-40 to -150)
What is the most altered RNA in prokaryotes?
tRNA.
What are the most altered RNA in eukaryotes?
both tRNA and mRNAs. mRNA have a 5’ cap structure attached to the 5’ end of mRNA
What is the point of the cap?
Protection against nuclease degradation, Facilitate translation by ribosomes and help mRNA exit the nucleus to cytoplasm
How is DNA in eukaryotes different from prokaryotes?
It is wrapped around positively charged proteins known as histones
What is the smallest unit of DNA wrapped around histones?
Core particle. It is the bead on the bead on a string model.
