Genetics Lecture 4 Flashcards
Does RNA polymerase require a template?
No.
During transcription, what unwinds the DNA?
RNA polymerase has helicase activity.
Define the promoter region for transcription initiation. Where is it found?
Site where RNA polymerase attaches. Immediately precedes the transcription initiation site, upstream of the gene.
The first site of transcription begins with +1. Where is the promoter region found?
Negative region.
What 3 things collectively make a gene?
The promoter, the RNA coding sequence, and the terminator.
What direction does RNA polymerase transcribe?
5’ to 3’.
Describe the prokaryotic promoter region, including where they are found and the sequence.
Has 2 conserved regions:
At -35 - TTGACA
At -10 - TATAAT
In prokaryotes, how does RNA polymerase attach to the promoter region?
A polypeptide called sigma factor binds to the two promoter regions, RNA polymerase binds at -55 to +20. Holoenzyme untwists the DNA at -10, and the sigma factor dissociates.
When RNA polymerase is bound to the DNA, where is the DNA untwisted, and by what? What is it called before and after holoenzyme action?
At -10 region by holoenzyme.
Closed promoter complex before untwisting, and opened promoter complex after.
As RNA polymerase moves forward transcribing, does the RNA remain bound to the DNA or does it dissociate?
Dissociates as RNA polymerase moves.
Which is faster, DNA polymerase or RNA polymerase, and why?
RNA polymerase is slower as it proofreads as it moves forward.
How many kinds of RNA polymerases are in prokaryotes vs eukaryotes?
Prokaryotes have one, eukaryotes have three.
What are snRNA?
Small nuclear RNA, that binds to some enzymes like telomerases.
What type of RNA makes up the most?
rRNA.
Which eukaryotic RNA polymerase transcribes mRNA?
RNA polymerase 2.
Where is the core promoter in eukaryotes? What is it called, and what kind of sequence is it?
Within 50bp upstream of +1. An initiator sequence called Inr, and has a TATA box.
Eukaryotic promoter regions have an additional 2 boxes in addition to the one found in the core promoter. Where are the two found, what are they called, and what sequence are they?
Promoter-proximal elements
CAAT box at -75
GGGCGG at -90
What mediates binding of RNA polymerase in eukaryotes?
Transcription factors.
How many copies of mRNA are made, just one or many?
Many.
How is transcription terminated in prokaryotes?
Stops as soon as the RNA polymerase reaches the termination sequence.
How is transcription terminated in eukaryotes?
Transcription continues for an additional 30bp. Is a special sequence that induces a termination hairpin formation, dissociating RNA polymerase.
Which of the two, eukaryotes and prokaryotes, have pre-mRNA?
Just eukaryotes.
What does pre-mRNA have at the polar ends that mature mRNA doesnt have? Why is it present?
An untranslated region that acts as a buffer, and later modifed to protect the mRNA from exonucleases.
What happens to the 5’ end of pre-mRNA? Whats unusual about it, and what does this facilitate?
A capping enzyme adds 2 methylated guanine molecules, an unusual 5’ to 5’ bond, which exonucleases cant break.
Facilitates ribosomal binding.
What happens to the 3’ end of pre-mRNA? What does this facilitate and inhibit?
A polyA tail of 50-250 adenine molecules are added.
Inhibits degradation, and facilitates export from the nucleus.
What do introns begin and end with that allows then to be spliced?
Begin with GU, and end with AG.
What mediates splicing, and what are they? How many are there? Name them.
Small nuclear ribonucleoprotein particles - SnURPs. Are snRNA associated with proteins.
Are 5 of them
U1, U2, U4, U5, U6.
Describe how splicing is carried out.
The SNURPs U1 and U2 recognise the GU and AG of introns and bind to them
The other 3 SNURPs bring the U1 and U2 together. The strands are then joined together.
Can translation occur at the same time as transcription in prokaryotes and eukaryotes?
Yes in prokaryotes only.
In eukaryotes, it must finish transcription, be exported, and spliced first.
