Transcription Flashcards
transcription 3 basic phases
-initiation
-transcription
-termination
in order for DNA to carry out functions what must it do
-be converted to RNA via transcription
promoters
-DNA sequences
-Guides transcription initiation
-resides upstram of henes
-in conclusion: DNA sequenxes bound by factors that promote transcriptional initiation
sigma factors
-binding of sigma factors to the promotor region (along iwth regulatory proteins) dictates whther a sequence acts as a promoteor and if promotor is active
sigma factors in transcription initation
-a special subunit of RNA polymerase called sigma factor binds DNA as an essential step in initiating transcription
-Bacteria encode various sigma factors that are produced under different conditions
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RpoD
-most commonly used
-recognizes two seuqences upstram of the transcriptional tartssite
-recognizes sequences at -36 and - 10 (pribnow box) upstream of the +1 site
the promotor region is where compared to the gene
upstream
RNA polymerase
bind to DNA template and makes an RNA copy of one of two strans
-Copied strand = coding strand (promotor dictates), othr strand = template strand
-builds RNAs 5’-3’
-
core enzyme
-bacteria
-5 subunits
-alpha (2 copies) beta, beta prime, omega,
-holoenzyme (type of core enzyme) also includes sima subunit
-core enzyme unwinds DNA to expose template and form transcription bubble
-Uses NTP as substrates and template strand as gyude
termination of transcription
-RNAP dissociates from DNA, stops making RNA and releases transcript
intrinsic (rho independent) terminators
-RNA forms hair pin strictire followed by a string of U reisdues
-U resideus act as a pause signal for RNAP and formation of hair pin fors RNAP off template
Rho dependent terminators
-Protein called Rho binds RNA as it is being transcribed and causes RNA polymerase to dissociate after it encounters certain sequences
3 major classes of RNAs
-mRNA - converted to protein via translation
-tRNA - functional RNAs used in translation process
-rRNA - functional RNA used in translation process
what is the majority of RNA
-rRNA and tRNA
mRNA contains
-both ORFs and UTRs
-ORFS are translated to protein
-UTR are part of the mRNA transcript that are not translated into protein
polycistronic
-mRNAs that encode multiple ORFs are polycistronic
-Genes are arranges in an operon
-Genes on an operon are cotranscribed
In a simple mRNA encoding a single open reading frame there is
-5’UTR - everything from first transcribed residue through the start codon of gene, contains ribsome binding site
-ORF - Start codon through stop codon
-3’UTR - everything from stop codon of gene through the final transcribed reisdue. often contains transcriptional terminator sequences
how is transcription different in eukaryotes
-eukaryotes have 3 RNA polymerases. RNA polymerase II produces mRNA
-eukaryotic RNA polymerases are more complex (12+)
-eukaryotic RNA polymerases required transciption factos to recognize promotors (bind to DNA sequqences adn recruit RNA polymerase)
-Eukaryoties do not use operans each genes has its own promotor
-eukaryotic primary mRNA transcripts contain protein coding exons and non coding introns, mRNA are processed to remove introns
-Eukaryotic have polyA tails addes and capped at 5’ end
-eukaryotic mRNA are trasncribed and spliced in nuclues and translated in cytoplasm
overview of transcript processing and transport om eukaryotic cells
transciption in archaea
-core aspects of archeal transcription are very. similar to eukaryotic transcription
-the archael RNA polymerase II from eukaryotes and has 11-13 subunits
-is also recruited to promotors using TF- many of which are related to eukaryotic proteins
-archaea also uses TATA boxes and TF that bind these elements and recruit RNA polymerase
similaritys of arahcea and bacteria transcription
-no 5’ cap
-no polyA taile
-mRNAs do not have introns and are are not spliced
-no nucleus transcription and translation often coupled like in bacteria
-archeaea use opens - multiple henes encoded by one RNA
-basically a less complex version of eukaryotic transcription
