transcription 2 Flashcards
what is an operon
a section of genes encoding for proteins related to each other, they are located adjacently and controlled as a single unit
within the promotor region of dna in prokaryotes, what are the 2 consensus DNA sequences and where are they located
- hexamer at -35 bps
- Pribnow box at -10 bps
what is a feature of the consensus DNA sequences and why does it have it
it is only in one dna strand so the polymerase knows which way to go
what are down mutations
mutations that decrease the promoter initiation and decrease the conformity to the consensus sequence
what is an up mutation
a mutation that can trigger transcription initiation
what are the other 3 bacterial promoters
up, extended and discriminator
what is a holoenzyme
an enzyme and a coenzyme
what are the 4 subunits of rna polymerase and what are their functions
- 2 alpha units for enzyme assembly
- beta and beta prime unit forms the catalytic centre
- sigma unit binds to promoter
why does the polymerase need the sigma region
it has strong binding strength for dna
what is sigma 70 used for
general use
what is sigma 32 induced by and what is different about it
high temperatures
will recognise different consensus regions
what is sigma 32 induced by and what is different about it
high temperatures
will recognise different consensus regions
what is sigma 54 induced by
lack of nitrogen
how can transcription be negatively regulated
repressors which bind to an operator site, which stops polymerase from binding
how can transcription be positively regulated
activators bind to a specific site and help polymerase bind
whats the repressor and activator of the lac operon
lac repressor and CAP-activating protein
what does beta-galactosidase do and what gene encodes for it
cleaves lactose into component sugars
lacZ
what does permease do and what gene encodes for it
transports lactose into cell
lacY
what does transacetylase do and what gene encodes for it
modifies lactose
lacA
what is lacI
regulatory gene
what happens in the lac operon when lactose is absent
the repressor is produced and it is bound to the operator site
what happens to the lac operon when lactose is present
allolactose will bind to the lac repressor and this will induce a conformational change in lacI so the repressor will not bind to the operator
what part of the lac repressor binds to the operator site and where
the lac repressors 2 dimers each bind to one operator site
how many operator sites does the lac operon have and which 2 can repressors bind to (2 lots of pairs)
3
-O1 and O2
-O1 and O3
what happens within the lac operon when glucose is low
cAMP will increase and this will activate CAP, meaning polymerase affinity will increase
what happens within the lac operon when glucose is high
cAMP will decrease and this means CAP is inactive, meaning polymerase not bind and the lac operon will not be activated
what is lactose converted to
allolactose
if there is low lactose and low glucose what will happen to the lac operon
there will be no transcription
how do we terminate transcription
there are 2 sections of symmetric dna and an A-T
this forms the stem and loop structure which stalls the polymerase
the A-T(U) region is weakly bonded so will cause unravelling
what is rho and what is rho-dependent termination
rho is a prokaryotic transcription protein
it will attach and move along the rna via atp hydrolysis and when the rna is stalled by the stem and loop, it will catch up and unwind the RNA-DNA pairing
