Transcription Flashcards
(46 cards)
Prokaryotic RNA polymerase
-multi subunit enzyme which recognizes nucleotide sequence ( promoter region ) at beginning of DNA length to be transcribed and also recognizes termination sequence
What direction is RNA made
5-3 antiparallel but complimentary to template ( antisense , minus ) and identical to coding strand ( sense , plus )
How is gene to be transcribed located
-through a sequence of nucleotides near gene called promoter region
Prokaryotic RNA POL structure
-has core enzyme with 5 subunits
1 2 alpha and omega - enzyme assembly
2 Beta prime - template binding
3 Beta - 5-3 RNA polymerase activity
-has s subunit ( sigma region ) which enables RNA POL to recognize promoter region
What is holoenzyme
S region plus core enzyme
Steps in transcription ( simplified )
1 initiation
2 elongation
3 termination
What is transcription unit and transcript
- region between termination and promoter
- initial product of transcription
Initiation.
-binding of holoenzyme to template ( via beta subunit )forming closed complex and unwinding of dsDNA ( a short length approx 14 bases ) to form open complex called transcription bubble
Consensus sequence
-idealized sequence in which bases shown at each Position is base most frequently encountered at that position ie length from initiation site
( not always the case )
Sequences recognized by s factors
1 -35 consensus sequence ( 5-TTGACA-3) centered at G 35 bases from initiation site. Initial contact point for Pol and forms closed complex
Numbering of bases left and right to initiation site and reason
- negative if left and positive if right
- regulatory sequence that control transcription are designated by 5-3 sequence on coding strand
Prinbow box
- 2nd consensus site wc holoenzyme moves onto next
- (-TATAAT-) centered at middle T 10 bases away from initiation site
- melting of dsDNA occurs here to form open complex transcription bubble
Elongation
- Unwinding continues mediated by POL which then synthesizes transcript from DNA sequence
- several short RNA strands made and discarded
When does elongation begin
When transcript exceeds 10 nucleotides
What happens after transcription done at a specific gene
-s subunit released and core can leave promoter and move along template in a processive manner.
What is sliding core of prokaryotic RNA POL
Itself
What occurs during transcription between RNA and DNA
-short pieces of DNA and RNA bind forming hybrids
How are nucleotides added and you where does energy come from
- ATP dependent which is acquired from triphosphate bonds which beak releasing energy and pyrophosphate
- nucleotides added with a phosphodiester bond inbetween 3 and 5 OH via ATP hydrolysis
When does transcription stop
-at termination signal which can be spontaneous or dependent on rho proteins
Rho independent termination
-sequence in DNA generates sequence in RNA that is self-complimentary and folds in on itself with a GC rich stem and loop Making a hairpin
What is beyond hairpin
String of U’s H2 bonded to A’s on DNA strand but weak forces so facilitates separation of RNA from DNA at hybrid
Rho protein properties
Participation of hexameric Rho protein with ATPase and helicase activities
Rho dependent
-rho binds with C-rich region in rho recognition site of RNA near 5 end and uses ATPase activity to move along chain it reaches POL paused at termination site and uses ATP dependent helicase active to break hybrid zone
Action of antibiotics in prokaryotic RNA synthesis termination
- some antibiotics Prevent bacterial cell growth by inhibiting RNA synthesis
- Rifampin inhibits transcription by binding to B subunit and prevents chain extension beyond : nucleotides
- Dactinmyosin binds to DNA template and prevents movement of RNA POL along DNA
