General mechanism of Transcription Flashcards
what is a coding strand
aka sense strand
5’ to 3’
has same sequence as RNA that’s produced
what is template strand
aka antisense strand
3’ - 5’
has complementory sequence to the RNA that’s producced
what does a promoter do
tells RNA Polymerase:
where to start transc
what direction to transc in
what are the sequences that an RNA pol recognises on a promoter
-10 = TATAAATG
-35 = TTGACA
only recognises this sequences then it knows what to attach to and which direction to go in
see onenote for diagram
what are the 3 phases of transcription
initiation
elongation
termination
main enzyme involved in transc
RNA polymerase
initiation
RNA pol binds to promoter
seperates strands for DNA
template strand used to make mRNA strand
elongation
using the template strand, complementary mRNA strand is produced
complementary nucleotides added to form strand
(remember not T but U in RNA strand)
termination
stop signal from terminator gene
mRNA released from trancription complex
this strand is called pre mRNA (not yet ready to leave nucleus
prokaryotic RNA polymerase enzyme subunits
sigma
2 alpha
2 beta (beta and beta’)
omega
prok RNA pol subunits function: sigma
promoter recognition
recognises the -35 and -10 boxes
prok RNA pol subunits function: alpha
assembly and transcription activation
prok RNA pol subunits function: beta
catalysis (adding nucleotides to growing RNA chain)
termination
prok RNA pol subunits function: omega
involved in assembly
folding
in some genes and not others
difference between RNA holoenzyme and core enzyme
holoenzyme - whole thing with all subunits
core enzyme - when polymerase starts transcribing, sigma subunit breaks off leaving the core enzyme (alpha, beta and omega units only)
why does sigma subunit need to break off`
only needed during inititation to detect the start codon
after this, the enzyme must turn non-specific for any particular sequence
so polymerase only has general affinity for DNA
euk RNA polymerase, the 3 types and their functions
pol I = makes ribosomal RNA genes
pol II = makes protein coding genes (mRNA)
and small nuclear RNA (snRNA)
pol III = transfer RNA (tRNA)
also, rRNA and snRNA
euk RNA Pol II features
large enzyme
~10 core subunitsk
how does euk rna pol II interact with the promoter sequence?
must be recruited by transcription factors
e.g. TF2D (aka TFIID so basically transcription factor for rna pol II)
what is function of TFIID and what is it made up of
allows the RNA pol II to recognise and bind to promoter site
TFIID is a multisubunit protein
made of these subunits:
TATA binding protein (TBP) = the bit that acc binds to the promoter site
and
TBP Associated factors (TAFs)
what is the TFIID similar to
similar sequence to the sigma subunit
promoters are very TA rich (similar to the -10 sequence in prok promoters)
other transcription factors needed in eukaryotes during initiation
TFIIA - helps TFIID bind
TFIIB - measures distance between core promoter sequence (the AT rich one) and the transcritption start site
other transcription factors needed and their general functions
TFII E, F, H, J and K
- blocks non specific binding of pol II to DNA (liek sigma)
- promoter clearance > starts to elongate and make chain
- helicase > unwinding the DNA
- procesivity > so once it starts, it continues to full transribe the chain
- DNA repair > scanning chain for errors and repairs it
RNA Pol I main elements
core element - contains transcription start site
Upstream control element (UCE)
these 2 bind with protein called Upstream Binding Factor (UBF)
which allows the DNA to kinda loop through
see onenote for diagram
