lecture 4 Flashcards
what are the steps in transcription?
- initiation
- elongation
- termination
what supports transcription?
- transcription regulators
- transcription factors
what is transcription?
copy the DNA into RNA
how many RNA polymerases do eukaryotes have?
3
how many RNA polymerases fo bacteria have?
1
what is the structure of bacteria RNA polymerase?
5 subunits
- 400-450 kDa
what is the function of RNA polymerases?
reading and transcribing a gene sequence into an RNA product
is RNApol a conserved structure?
RNA polymerase general architacture and catalytic function is conserved across the three domains of life
what is the action of bacterial RNA pol?
- bacterial RNAP has a crab-cpaw appearance that opens and closes during transcription
- the incoming dsDNA goes into the cleft, becomes unwound and is transcribed into a strand of RNA
- the exiting DNA comes out in a perpendicular direction
what is the structure of the core of RNA polymerase?
parts of the beta and beta’ and the two alpha subunits
what is the structure of the jaw-lobe of RNA polymerase?
parts of the beta subunit
what is the role of sigma in bacterial RNA polymerase?
participates in recognizing the promoter and initiate transcription
where does the sigma factor bind on bacterial RNA polymerase?
to the cleft
what happens in the initiation stage of transcription?
RNAP binds to the promoter, near the beginning of a gene transcription bubble
what happens in the elongation stage of transcription?
RNAP reads the template strand one base at a time
RNAP buikds a complementary RNA molecule
what happens in the termination stage of transcription?
Terminators signal that the RNA transcript is complete RNAP is released
what is the bacterial promoter region in a gene?
specific dsDNA region where the RNAPol binds
promoter regions have very conserved structure
what are the regions of the promoter of a bacterial gene?
UP element: -37 to -58
the -35 element: -35 to -30
the extended -10 element (Ext): -17 to -14
the -10 element: -12 to -7
the discriminator element (Dis): -6 to -4
*the exact position of each element may vary
how does RNAPol recognize the bacterial gene promoter?
specific elements are recognized by individual domains of sigma factor and alpha-RNAPol
where does transcription start in the gene?
at the +1 bp
what is the composition of E.coli during growing conditions?
55% protein
10% lipid
3% DNA
20% RNA
<1% mRNA
why is RNA found in much higher quantities within the bacterial cell than mRNA?
mRNA has a half-life od 3-8mins
RNA has a half-life of days
what is E.coli house keeping sigma factor?
sigma 70
what is the role of sigma70 (house keeping sigma factor)?
has lots of domains, each responsible for recognising a section of promoter
- sigma 70 recognizes most promoters
what are the domains of sigma70?
3&4 - correct position of the promoter
1&2 - open complex
what mediates binding of RNAP to the promoter?
initiation factor
what is the role of sigma factor in initiation of transciption?
ensures the correct orientation of the dsDNA in the RNApol
what does elongation of the RNA transcript occur?
once the sigma factor is released
what is the role of RNAPs catalytic core?
RNAP catalytic core is capable of RNA polymerization
what eukarotic polymerase is similar to bacterial RNA pol?
Pol II
what is the structures involved in elongation?
Initiation factors are exchanged for elongation factors during the early stages of RNA synthesis
in E.coli- initiation factor (sigma 70) and elongation factor (NusG) bind to the same RNAP region
what happens during elongation?
DNA-RNA hybrid of 8 to 9 base pairs is formed in the transcription bubble
The downstream DNA is not yet transcribed; the upstream DNA has regained the duplex form
what is the function of backtracking in elongation during transcription?
incorrectly incorporated nucleotides can be excised
what is the role of the rudder loop in elongation?
separates DNA
what maintains the transcription bubble in elongation?
a series of loops
where is the active site of the RNApolymerase?
the active site is located at the floor of the cleft
when does the elongation phase start?
after RNAP synthesizes 9-10 RNA nts, it escapes from the promoter region
what occurs during the termination of bacterial transcription?
intrinsic termination- DNA and RNA sequence
the helicase Rho associate with C-rich RNA sequences and expeles RNAP from the DNA
the helicase Rho engages with NusG, NusA, and RNAP during transcription elongation
RNAP dissociation from the DNA
