transcription Flashcards
(109 cards)
list 3 ways that RNA polymerases are different from DNA polymerases
RNA pol adds ribonucleotides (U instead of T), doesn’t require a primer, lacks 3’-5’ exonuclease proofreading
T or F: RNA pol requires a primer to work
false; it doesn’t need a primer
T or F: the polymerization method is the same for DNA pol and RNA pol
true
describe the polymerization mechanism for RNA pol
nucleophilic attack by the 3’ OH on the phosphorous of an incoming NTP. Pyrophosphate exits as NMP is incorporated into the growing RNA strand. Mg2+ facilitates the nucleophilic attack + the other helps displace the leaving PPi
in which direction is the template strand copied
3’-5’
describe the general shape of the bacterial RNA pol
5 core subunits in a claw-like shape
what does the sixth subunit of bacterial RNA pol do + what is it’s name
sigma subunit: binds transiently to the core and helps direct it to specific DNA binding sites
T or F: RNA pol only binds to DNA in the presence of the sigma subunit
true
list the components of the holoenzyme
core + sigma subunit + DNA
where on the DNA will the sigma subunit bind during bacterial initiation
it binds to promoters upstream of the genes that need to be transcribed
which two promoter sequences does the sigma subunit bind to in bacterial initiation
-10 and -35
why are the -10 and -30 called consensus sequences (ie why consensus specifically)
bc these sites are usually similar across different promoters
describe why promoters establish a basal level of gene expression for every gene that can be upregulated or downregulated
mutations in promoters can greatly lower RNA pol binding and transcript initiation
what happens to the DNA when sigma binds to the consensus sequences in the promoter in bacterial initiation
DNA bends
what happens once sigma binds to promoter and DNA bends? (ie what is the result of this)
allows the RNA pol to interact with both the -10 and -35 regions at the same time
in bacterial initiation, describe what occurs once RNA pol is bound to both -10 and -35
the upstream promoter (UP) binds to the core RNA pol
the UP is rich in which bases
AT
T or F: in bacterial initiation, the upstream promoter (UP) binds to the sigma subunit
false; it only binds to the core RNA pol, not the sigma subunit
bacterial initiation: describe the events once everything is bound (consensus sequences, RNA pol, UP)
sigma binds to promoter and brings the polymerase core with it. First a closed complex is formed where DNA is still wound, then an open complex is formed when DNA begins to unwind near -10
bacterial initiation: where does DNA begin to unwind
-10
when bacterial initiation has started via conformational changes in RNA pol, what happens once RNA pol clears the promoter
sigma dissociates and NusA protein binds in its place
bacterial elongation: once sigma dissociates, which protein binds in its place
NusA
which step in the process signifies the start of bacterial elongation
once RNA pol has cleared the promoter, we’re now in the elongation stage
why is bacterial regulation tightly regulated
if RNA pol falls off too early, it has to restart the transcript all the way back at the promoter
