The Process of Transcription Flashcards
What does RNA pol not need to use but DNA pol does?
RNA pol can start a new RNA chain without using a primer
Does the whole strand open during translation?
No the DNA only opens within the RNA polymerase (small section at a time)
What end of the mRNA leaves the polymerase first?
The 5’ end leaves while the nucleotides are being added to the 3’ end
What is the stretch of DNA that is transcribed into an RNA molecule called?
A transcription unit
How many types of RNA polymerase do bacteria have?
Bacteria have one type
What does the RNA polymerase do in bacteria?
It synthesizes mRNA as well as other types of RNA
How many types of RNA polymerases do eukaryotes have?
Eukaryotes have three different types
What RNA pol synthesises mRNA in eukaryotes?
RNA pol II
What does RNA pol I and II do in eukaryotes?
They synthesis other types of RNA other than mRNA
Write a note on RNA polymerase in prokaryotes.
3
Composed of five polypeptide polymerase core enzymes
a, a’, B, B’ and sigma -> all have unique roles
The subunits assemble each time a gene is transcribed and disassemble once transcription is complete
What does the sigma subunit of RNA polymerase do?
2
It’s only involved in transcription initiation
It ensures that mRNA is synthesised from an appropriate site
What is RNA polymerase called when it is comprised of all five of it’s subunits?
Haloenzyme
What does the sigma factor identify?
It recognises the promoter sequence of DNA
When does the sigma subunit release?
When polymerase has synthesised 10 nucleotides
Do all sigma subunits respond to the same promoter?
No different sigmas respond to different promoters
When does RNA polymerase stop?
When it comes across a terminator or stop site
What happens when RNA polymerase comes across a terminator site?
(3)
RNA polymerase halts
The DNA template and the newly made RNA chain is released
RNA pol then reassociates with the sigma factor and searches for another promoter to begin the process of transcription again
What are the three main steps in transcription in prokaryotes?
Binding and initiation
Elongation
Termination
What must happen at the end of transcription in eukaryotes?
mRNA processing must occur before RNA leaves
How does initiation of transcription work in eukaryotes?
4
A collection of proteins called transcription factors are needed
They mediate the binding of RNA pol II to promoter
A promoter DNA sequence (TATA box) is crucial for forming the transcription initiation complex
Complex then moves Pol II to start site of gene and begins to polymerise
What are transcription factors?
A collection of proteins that mediate the binding of RNA pol II to promoter
What is needed to form the transcription initiation complex?
A promoter DNA sequence known as a TATA box
What is the main difference between transcription in Eukaryotes vs Prokaryotes?
RNA pol II in eukaryotes doesn’t need a sigma factor but does need transcription factors
