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Transcription: DNA to RNA in prokaryotes (steps in prokaryotes (initiation…
Transcription:
DNA to RNA in prokaryotes
steps
in prokaryotes
elongation
in prokaryotes, transcription can occur simultaneously with translation
rate is 20 base pairs per second in euk.
termination
Rho dependent
factor rho binds to the growing mRNA strand and moves towards RNA polymerase, Rho-termination sequence (
in DNA
) causes RNA polymerase to stop, factor rho catches RNA pol and that causes the release of mRNA
Rho-independent
this is dependent on the secondary structure of RNA
, terminator sequence is a G:::C rich palindrome prior to 6-7 Us
initiation
RNA polymerase complex recognizes specific DNA target sequences
promoters are usually just upstream (5') to the start of the transcription site
promoters
have
conserved consensus sequences
; the most of which is called the
core
promoter examples:
TATAAT/Pribnow Box, -35 Box
initiation in prokaryotes
sigma
binds to
RNA polymerase
(core enzyme) = holoenzyme
sigma
binds to TATAAT and -35 boxes, and opens the strands at the TATAAT box
RNA polyerase does not need a primer
after ~10 nucleotides sigma leaves, RNA polymerase keeps creating mRNA
clinical correlate:
rifampicin
is an antibiotic that treats TB by binding to bacterial RNA pol so it can't make mRNA
comparison to eukaryotes
DNA is in a "looser" conformation to allow access of key enzymes/proteins (fewer nucleosomes)
transcription factors
must bind to promoter sequence prior to RNA polymerase
there are 3 different types of RNA polymerase