4-1: Transcription Flashcards
Enzyme involved in transcription
RNA polymerase
Why must DNA be converted to RNA
DNA encodes genes but is inert
Needs to be RNA to carry out fxns
Two strands in transcription. Which one is copied
Coding (copied) strand
Template strand
What subunits make up RNA polymerase (core enzyme)
alpha subunit x2
Beta
Beta’
Omega
What is the holoenzyme made up of, what does it do
Sigma factor (subunit)
Recognize promoter sequences
What does the core enzyme do
Unwinds DNA, forms transcription bubble
Builds RNA chain one nucleotide at a time
When is transcription terminated
When RNAp encounters a transcriptional terminator it dissociates
What are the transcriptional terminators
Intrinsic (rho-ind) terminators: RNA hairpin forms, followed by string of ‘U’ residues (pause signal). Hairpin forces RNAp off
Rho-dependent terminators: protein called Rho binds RNA as it is transcribed, causes RNAp to dissociate after encountering certain sequence
What is the terminator involved with hairpin formation
Intrinsic (rho-independent) terminator
What initiates transcription
DNA sequences called promoters
What dictates whether or not a region acts as a promoter
Sigma factors
Regulatory proteins
What is the most common sigma factor
sigma^70 aka RpoD
What sequences does RpoD recognize
TTGACA ~35 bp upstream from +1 (start site)
TATAAT ~10 bp upstream of +1 site
Another name for the TATAAT sequence
Pribnow Box
What are the three major classes of RNAs
Messenger RNA (mRNA)
Transfer RNA (tRNA)
Ribosomal RNA (rRNA)
What are the functions of tRNA and rRNA
Functional RNAs used in the translation process
What is mRNA
converted to protein during translation
What kind of RNA makes up ~95% of a growing cell
rRNA, tRNA
what are the two regions of mRNA
Open reading grames (ORF’s: translated)
Untranslated regions (UTRs)
What are polycistronic mRNAs
mRNA that encode multiple ORFs
How are polycistronic mRNAs arranged. Why?
Into an operon. So they can be cotranscribed
The ORF spans from…
The start codon (e.g. ATG) to the stop codon (e.g. TAA)
The 5’UTR spans from…
+1 to start codon. Contains ribosome binding site
3’ UTR spans from…
Stop codon to final transcribed residue. Contains transcriptional terminator
How is transcription different in eukaryotes?
3 RNA polymerases (RNAp 2 produces mRNA)
More complex RNAp (12+ subunits)
Use of transcription factors by RNAp to recognize promoter
No operons
Polyadenylated 3’ end, capped 5’ end
Briefly describe transcription in archaea
Similar to euk
RNAp resembles RNAp 2 from euk
11-13 subunits in RNAP
Transcription factors
BUT similar to bacteria because simple
NO 5’ cap, NO poly A tail, no nucleus
Operons
mRNA that encode multiple ORF are…
polycistronic
