3.9 transcription review Flashcards
how is RNA different than DNA?
- has uracil instead of thymine
- hairpin loop most common structure
- very prone to modifications/processing
how is RNA polymerase different than DNA polymerase ?
- no primer needed
- much slower
- can synthesize bases de-novo
- has its own helicase activity
what are the 4 basic steps of transcription?
- initiation
- elongation
- termination
- post-transcriptional modification in eukaryotes
how many subunits are bacterial RNA polymerases made of?
6
what are the two forms of bacterial RNAP
core (a2bb’w)
Halo (core + sigma)
_______ bacterial RNAP can bind to any DNA and start transcribing. ____ binds to core, converts it to holoenzyme, and has specificity
Core
sigma
Core RNA is useless until what?
sigma binds
promoter regions usually have what two specific regions in them?
-10,-35
if you add nucleotides you might not be able to see the __________ and promoters may not be able to bind
-35 and -10 regions
every bacteria has how many sigma factors?
multiple
steps of transcription initiation in bacteria?
- sigma binds to RNAP
-RNAP binds to promoter region
-formation of open complex - transcription starts
-initiation ends after first inter-nucleotide bond forms
what are some factors that affect transcription initiation?
- promoter strength (how likely will they be recognized)
- dna supercoiling (can. hide or open promoter seq)
-UP element
does RNAP transcribe at a constant rate?
no!! it pauses every ~100 nucleotides
what are two ways that RNAP are modulated?
-hairpin pause (hairpin is formed, factors must come relieve it before RNAP can continue)
-backtrack pause (the way is blocked, must backtrack for Gre/Pi to chew away before RNAP can start again)
what happens during transcription termination?
- cessation of elongation
- release of transcript from ternary complex
- dissociation of RNAP from complex
-zipping back of DNA double strands
what are the 2 mechanisms of transcription termination?
factor independent and factor dependent
_______ is a polycistronic RNA that encodes for multiple gene products
an operon
rRNA is transcribed as a ______ transcript
30s
you need a 1:1:1 ratio of 16:23:5s rRNA for what to happen?
nuclease processing
every tRNA has what?
- G at 5’ end
- ends with CCA
bacterial RNAP can bind to _________ on its own but needs ______ for specificity
promoters, sigma
bacterial RNAP has very little post-translational modifications except what?
rRNA and tRNA
what does eukaryotic RNAP I transcribe?
most rRNA genes
what does eukaryotic RNAP II transcribe?
protein coding genes, miRNA genes, some genes for small RNAs
what does eukaryotic RNAP III transcribe?
tRNA, 5s RNA
which promoters are more well defined: eukaryotic or prokaryotic
prokaryotic
_____ are areas of DNA that dont code for a protein
intron
_________ help euk RNAP bind to the promoter
general transcription factors
______ is a downstream promoter element and is most common when TATA is missing
DPE
_____ is the initiator element
Inr
_____ is the TFII recognition element
BRE
RNAPII cnat bind by itself and needs a what ?
general transcription factor
_____ is surrounded by a GC-rich region and is the only upstream promoter with a fixed location
TATA box
does eukaryotic RNAP also need to pause?
yes
_____ is a TF kinase that phosphorylates CTD of RNAPII to activate elongation
P-TEFb
what catalyzes eukaryotic RNAP termination?
Cleavage and polyadenylation complex (CPA) recognizing Poly A signal (this dephosphorylates RNAP)
what are some euk RNA modifications?
-5’ cap
-3’ tail
-splicing
what is a 5’ cap and whats its function?
- addition of methylated G7
- protects 5’ mRNA
- allows for proper ribosome positioning
- helps with export to cytoplasm
- promotes intron excising
what does the Poly-A tail do?
- gives mRNA stability
-facilitates export to cytoplasm
-helps with ribosome positioning
what shows that an RNA is mature?
having a 5’cap, 3’ tail, and introns cut out
what are the 2 types of splicing?
lariat, transesterification
_______ make up spliceosomes that help process nuclear mRNA (introns removed in lariat pattern)
SNRPS
_______ can produce a diversity of mRNAs from a single gene by arranging coding sequences
alternative splicing
______- is transcribed as a 45S transcript by RNAPI in the nucleus
rRNA
______ is processed as a 100nucleotide precursor by RNAPIII and is processed and modified before mature
tRNA
RNAP binding at promoters may require ________
transcriptional factors
promoters contain ____ elements and sequence for specifying tissue specificity
cis
