Transcription Flashcards
what is the central dogma made up of
DNA (storage and database), RNA (instructions), Proteins (products)
what is transcription
making RNA from DNA
what do RNA polymerases do
transcribe the template strand into a strand of RNA
what determines where and when transcription occurs
promoters
what is true of polycistronic bacterial mRNAs
they have a single promoter, contain multiple ribosome binding sites (RBS), usually contain genes in the same pathway or operon, code for multiple proteins
what does RNA polyermase do
makes polymers of RNA using DNA as its guide
what can RNA polymerase do that DNA polymerase cannot
it is capable of making dimers of the nucleic acid that it polymerizes
how is RNA polyermase different from DNA polymerase
it does not need a primers, does not need a helicase, is less processive (does not go as far), has no proofreading ability
why do bacterial RNAP require sigma subunits
allows the holoenzyme of RNAP to interact stably with DNA at the promoter
what does sigma 70 do for RNAP
binds to the core enzyme of RNAP to create the holoenzyme which can then bind to DNA, find a promoter and create RNA
what is the -35 sigma 70 promoter sequence on the coding strand / what is the -10 sigma 70 promoter sequence on the coding strand
TTGACA / TATAAT
what do promoters do
they are a sequence of DNA that have several distinct regions that the RNA pol holoenzyme recognizes to start transcription
what is the optimal distance between -35 and -10 sequences
16-18 bp - highly conserved
what is the difference between a strong promoter and a weak promoter
strong promoters look more like the original sigma 70 sequence, weak promoters are not super identical to the original sigma 70 promoter sequence
what are consensus sequences of promoters
they highlight the importance of each base in the sequence - how highly conserved it is across species
how many parts does sigma 70 have / what do they do
it has 4 parts / they dramatically change what is expressed by the cell
during the elongation phase of transcription can the RNA pol knock off other proteins bound to the DNA
yes it can - it the DNA-RNA complex is very stable (strong) and very fast
why does RNAP not use proofreading
because so many RNAs are being made and a mistake in the RNA is not heritable so it really does not matter - proofreading also costs a lot of energy while slowing the polymerase down
why can transcription occur at the same time as replication (if it is following)
there are periodic pauses during the transcription phase
what is a terminator
a sequence at which RNA polymerase stops RNA synthesis
what are the three steps of termination
- the Core RNAP pauses 2. RNA-DNA duplex falls apart 3. RNA pol leaves DNA & releases RNA
what are two types of termination
Rho-independent (intrinsic) and Rho-dependent
what does intrinsic termination need
hairpin in RNA and a poly-U site (only RNA)
what does rho-dependent termination require
rho protein, c-rich region
where does translation of mRNA occur in bacteria / what does that mean for transcription and translation
in the cytosol / means transcription and translation can occur at the same time
what does Rifampicin do / what is it used to treat
binds to the beta subinit - blocks the channel for mRNA to exit the RNAP / used to treat tuberculosis
what does rifampicin not affect
does not affect already transcribing RNAPs
