w5 slides fc Flashcards
2 types of genes that when transcribed…
- the resulting rna encodes a protein
- the resulting rna functions as rna and may NOT be translated into protein
rna polymerase function
opens up helix as it transcribes and adds ribonucleoside triphosphate
transcription cycle
steps:
-sigma factor binds to RNA polym. and finds PROMOTER sequence (signals start of transcription)
-localized unwinding of dna, a few short RNAs synthesized initially and then RNA polym. clamps down (sigma factor released and NO primer involved)
elongation
termination and release of RNA
-after terminator sequence is transcribed, sigma factor rebinds and process restarts
on the 5’ strand, on promoter sequence, what’s the sequence at -35 called
upstream
tata box at -10
true or false: you can use different sigma factors to recognize different promoter sequences
true
in a terminator sequence, the GC rich regions…
fold into hairpin loop
-pull messenger rna away from dna template
-H bonds b/w dna and rna (2 base pairs_
—>causes the loop
what happens during termination
rna polymerase releases and binds another sigma factor
rna synthesis vs elongation mode of rna polymerase
rna synthesis = relatively inefficient
elongation mode = highly processive
what are some of the characteristics of rna termination signals?
-hairpin structure formed as a result of GC rich sequences
-AT rich DNA sequences following hairpin sequences
how do termination signals help dissociate rna transcript from polymerase
-disrupts H bonding of new mrna transcript with dna template
prokaryotic gene expression
no nucleus= why bacteria replicate so quickly
-their transcription and translation are NOT separated
mRNAs
messenger rnas, code for proteins
rRNA
ribosomal rna, form the basic structure of the ribosome and catalyze protein synthesis
tRNA
trnsfer rna, central to protein synthesis as the adaptors between mRNA and AA
function of rna polymerse ll
ALL protein-coding genes, miRNA geenes, plus genes for other noncoding RNAs (e.g. those of the spliceosome)
eukaryotic rnap ll vs. bacterial rnap structure
bacterial rnap has 5 subunits, eukaryotic rna pol ll has 12
rna pol ll has special carboxyl terminal domain (CTD) not found in bacterial or other eukaryotic rnaps
eukaryotic vs bacterial rna polymerases
eukaryotic rna polymerases require proteins to help position them at the promoter called: transcription factors
these factors fulfill a similar role to the SIGMA subunit of the bacterial rna polymerase
eukaryotic rna polymerases need to deal with chromosomal structures
tata box function
the sequence tata is highly conserved, found 30 bp UPSTREAM from start site for transcription
-helps position rnap ll
steps in the initiation of transcription
binding of tata binding protein subunit of TFIID to tata box sequence
-mobilizes the binding of TFIIB complex adjacent to tata box
other transcription factors bind
-rnap ll together with other TFs, will be able to bind in correct orientation at transcription start site
-helicase activity and phosphorylation of C-terminal domain (CTD) of RNAP ll
–both jobs performed by TFIIH
transcription steps simplified
-tbp and tfiid bind tg onto helix and helix bends
-acts as helicase nd unwinds the double strnded helix = helicase domin
then kinase domain allows phosphorylation
mediator
assembles nd coordinates activator protein
steps in the initiation of transcription
- TBP a subunit of TFIID binds to TATA box promoter in the minor groove, bending and distorting the DNA
- this attracts other transcription factors, which help to orient and bind RNAP ll to the DNA
- the helicase activity of TFIIH uses atp to pry apart DNA strands at transcription start site
- TFIIH also phosphorylates the C-terminal domain of RNA polymerase ll, activating it so that transcription can begin
carboxyl terminal domain
found on largest subunit of rna polymerase ll
-tandem repeats of 7 AAs
how is rna polym ll activated
phosphorylation
