Transcription (Chapter 36) Flashcards
(37 cards)
Difference between RNA and DNA synthesis?
- RNA doesn’t need primers.
- Ribonucleotides used.
- One strand is used.
- RNAP has OWN helicase activity.
- RNAP does not have proofreading ability.
Name the types of small RNA and their function.
snRNA - involved in pre-mRNA ripening snoRNA- involved in chemical modifications of tRNA etc miRNA - prevents translation siRNA - degrades RNA molecules piwiRNA - protects against transpoons.
Which direction is template strand read in?
Which direction is RNA Synthesised?
Read in 3-5.
Synth in 5-3
What makes up the Prokaryotic RNAP?
What does each subunit do?
two alpha subunits.
1 b’ and b subunit.
w(omega) subunit.
alpha binds to regulatory sequences.
b - binds to mg2+ to form the catalytic subunit which forms PDEB
b’ - holds the DNA template.
What is the importance of the Sigma Subunit in Prokaroyes?
It binds to the RNAP’s core to form a holoenzyme.
This then binds to specific promotors.
SO DIFFERENT SIGMA FACTORS HAVE DIFFERENT AFFINITIES TO DIFFERENT PROMOTORS.
Steps of Transcription cycle?
1) closed promotor complex
2) open promotor complex
3) chain initiation
4) Promotor clearance
5) Chain elongation
6) Termination
What is happening during the: Closed Promotor complex?
RNAP binds to DNA and is looking for a promotor.
What is happening during the: Open Promotor complex?
What else do we call the open promotor complex?
RNAP had bound to the DNA, causing it to melt and unwind.
We call it the “initiation complex”
What happens during: Chain Initiation?
RNAP catalysed the coupling of the first base (usually purine) with second.
What happens in: Promotor clearance?
The RNAP undergoes a conformational change after adding 10ish Nucleotides. and moves away from the promotor.
What happens during: Chain Elongation?
As RNAP moves, DNA unwinds infront, reanneals behind.
Nucleotides added to 3-OH of the Nascent RNA.
Importance of Ubiquitious Pyrophosphatases?
It breaks ppi into pi.
ensuring irreverisibility in every cycle of polymerisation
Termination in Prokaryotes?
Rho-independent:
- palindromic sequences
- cause hair loop
Rho-dependent:
Rho is an ATP dependent RNA stimulated Helicase.
When RNAP bound to -35BP of DNA promotor what does it form?
Closed complex.
Bacterial promotor?
-35 and -10.
- 10 (TATA BOX):
- AT rich region
- Has low melting temperature thus allows easy dissociation of the two strands.
Explain the Rho-dependent Signals?
They consist of inverted repeats.
Followed by AT.
They cause a hairpin to form, which slows down RNAP allowing Rho (an ATP depedent RNA stimulated helicase) to bind to it.
Where is Methylated Cytosine most commonly found?
In regions of high transcription activity.
1) How many Eukaryotic RNA Polymerase can be found?
2) What are their products and how are they affected by al-amantin?
1) 3RNAP and 1 Mitochondrial RNAP.
RNAP1: Forms rna like 28s, 5,8s, 18s
Not sensitive to a-amantin
RNAP2: Forms mRNA and small RNA
It is very affected by a-amantin
RNAP3: Forms tRNA and 5s rRNA, mitochondria RNA
It is slightly affected by a-amantin
What is the location of TATA box in Eukaryotic Promotors?
-25bp
What is the location of Inr in Eukaryotic Promotors?
-3 to +5
What is the location of DPE in Eukaryotic Promotors?
+25Bp
What happens in a mutation of TATA?
A mutation in Tata box causes a decrease in transcription.
What are GC and CAAT Cis elements? What are they bound by?
GC and CAAT are found upstream.
Upstream cis-elements tend to affect the frequency of transcription.
GC bound by SP1 (has a zinc finger motiff)
CAAT bound by CTF
What is TATA box bound by?
Tata box is bound by TBP.
TBP is found in: - TFIID
- SAGA
- P-caf
