Flashcards in EC L2a Deck (18)
bacterial core enzyme RNAP made of 5 subunits
2 x Alpha
1x w for omega
bacterial holoenzyme RNAP is made of 5 subunits
core's 5 subunits plus *O* for sigma
info card about core and holoenzymes
core enzymes start randomly on native and foreign DNA so in other words does not know where to start
holoenzymes makes random starts on foreign DNA but makes specific starts on native DNA and so produces significant RNA products because it is able to find promoters
what enables RNAP to recognise promoters?
holoenzyme recognises the promoter and initiates transcription, almost immediately the sigma factor comes off and the core enzymes continues elongation and completes it
RNAP subunits functions
Beta- active site processivity
Alpha- DNA binding (non specific)
Omega- Enzyme assembly
Sigma- Promoter recognition which is responsible for the specificity of it binding to DNA
how many sigma factors do bacteria have?
what regulates gene expression in bacteria?
initiation of transcription: transcription bubble, how many bp are opened in the transcription bubble?
17 bp are unwound and opened
initiation of transcription: transcription bubble... what opens the promoter?
info on initiation stage of transcription
Initiation stage: - holoenzymes binds to the DNA recognizes the promoter, and it starts to unwind the promoter. there are 17 base pairs of DNA (approx, 2 helical turns).=> holoenzyme opens up the promoter and initiates transcription. this is referred to as the transcription bubble as seen on the slide.
info on elongation of transcription
as the transcription bubble moves along (from left to right) the sigma factor comes off, and the core enzyme will start transcribing one of the strands. The transcript bubble will move along the DNA.
=> when the transcription bubble wants to move along the DNA, the DNA will start to unwind , but it must coil up in the opposite sense somewhere else round that circle ( this is called rewinding), this can be prevented by cutting strands and pattern a strand from another. The number of times one strand goes across the other one is constant unless the strands are stopped from being cut, however, RNA pol doesn’t cut strands.
info on termination of transcription
Transcription termination. RNA polymerase will keep transcribing until it gets signals to stop. The process of ending transcription is called termination, and it happens once the polymerase transcribes a sequence of DNA known as a terminator.
where do eukaryotes have RNAP
3 in the nucleus
1 In the mitochondria which is diff than the nucleus ones
2 in the chloroplasts
pol I- makes large rRNA
pol II- makes mRNA
pol III- makes small tRNA
where nuclear RNA's are located in the nucleus
pol I which makes rRNA's are made in the nucleolus the others are not
info on eukaryotic RNA pol
RNA pol I has 14 different subunits; RNA pol II has 12; RNA pol III has 17.
These nuclear RNAPs each possess subunits that are related (but not identical) to the 5 subunits of the bacterial core RNAP but these counterpart proteins still differ between the nuclear RNAPs. In summary, although there are clear similarities between the different nuclear RNAPs, they have few subunits in common. Thus, RNA pol I with 14 subunits is not simply RNA pol II (12 subunits) plus 2 extras.