Transcription Flashcards
common types of RNA
-mRNA
-tRNA
-rRNA
Eu RNA
pre-mRNA
small nuclear RNA
small nucleolar RNA
MicroRNA
Pro RNA
CRISPR RNA
template vs coding strand
RNA synthesis is complementary and anitparallel to template strand while coding strand is not transcribed
Pro Initiation of transcription (summary)
promoter recognition
formation of transcription bubble
Creation of first bonds between rNTPs
Escape of transcription apparatus from promoter, sigma factor disassociates
Bacterial promoter regions
-35 consensus sequence
-10 consensus sequence (pribnow box)
Iniation of transcription in Pro (full)
-sigma factor associates with core enzyme to form holoenzyme
-Holoenzyme binds to -35 and -10 consensus sequence
-Holoenzyme binds to promoter tightly and unwinds double strand
-a rNTP complementary to base at start site is first nucleotide in RNA
-Two phosphate groups are cleaved from each subsequent rNTP which is then added at 3’ end of growing molecule
-The sigma factor is released after 10 nucleotides are transcribed
DNA bending in Pro initiation
-RNA Pol first forms a closed complex where DNA is not unwound at -35 region
-Open complex forms at
-10 site where it is unwound
-Mg further unwinds DNA from -12 to +2
elongation of transcription
Nuclophilic attack of 3’-OH of first nucleotide on the alpha phosphate of the second nucleotide forms a phosphodiester bond
-as process continues, DNA is continuosly unwound in a transcription bubble
sigma factor disassociates after first 10 nucleotides
Topoisomerase and Gyrase
Topoisomerase removes negative supercoils behind transcription bubble while gyrase introduces negative supercoils
RNA Pol backtracking
when RNA Pol reaches a site that is difficult to transcribe it may pause or shift backwards
Transcription can then continue by either Pol sliding forward or by cleaving of non-base-paired part of transcript to create a new 3’-terminus
Rho-independant termination
-Terminator consists of inverted repeats followed by a string of 6 adenosine nucleotides
-Inverted repeats are transcribed into RNA
-The string of Us cause the RNA pol to pause
-Inverted repeats fold into a hairpin which destabilizes RNA-DNA pairing
-the RNA transcript seperates from template which terminates transcription
RHO-dependant termination
-Rho binds to rut site and move towards 3’ end
-RNA Pol pauses when it reaches terminator sequence
-Rho catches up and uses helicase activity to unwind RNA-DNA hybrid and bring transcription to an end
Differences between Pro and Eu transcription
Eu RNA pol
Initiatation of Eu transcritption (summary)
Eu transcription initiation regions
Eu transcription initiation
Termination of Eu transcription
Eu mRNA processing steps
Addition of 5’ Cap
Polyadenylation of mRNA
Alternative splicing
RNA interference
