Biochemistry - Transcription Flashcards
What are the two steps of protein synhesis?
Transcription
Trnaslation
RNA polymerase
This is the the primary gene expression enzyme transcribing DNA into RNA.
What does RNAP II do?
Primary eukaryotic polymerase for all protein-coding genes and non=protein RN like nuclear RNA.
What does RNAP III do?
Transcribes tRNA genes and the 5S component of rRNA.
What is gene regulation mediated by?
Promoters like enhancers and silencers.
Promoters
Regulatory regiosn where polymerases or TFs bind to initate gene transcription
What region do RNAP bind?
The TATA box of the promoter.
TATA box
This defines transcription direction and indicates the DNA strand to be read
How do enhancers and silencers work?
Bind the TATA box and regulate their activity.
What is required of the chromosome for transcription?
Chromatin remodelling complex opening of nucleosomes.
What are the five TF mediating RNAPII function?
TFFIIB, E, D, F and H
Why does so much cell variety exist in organisms?
Due to the variability by gene regulatory networks like enhancers and silencers.
Gene Regulatory Networks
Molecular regulators interacting with TFs and genes to regulate mRNA expression
Enhancers
Amplify gene expression, can be up to 1 million base pairs away, but on average 100-1000 bp.
Intergenic
In between active genes
Intronic
In between exons, on the introns.
Where are enhancers, super-enhancers and silencers found?
Intergenic and intronic regions
What happens in initaiton of PS?
TBP brings promoter DNA into contact with TFIIB of RNAPii, destabilising DNA to prepare elongation.
What happens when RNAPII first contacts promoter region?
It folllows until 25-30bp from TATA, where transcription site near polymerase active site, where TFIIE and H is recruited.
TFIIH
Destabilises DNA duplex to allow thermal unwinding forming transcription bubble.
Transcription bubble
A complex formed when a limited portion of the DNA double helix is unwound.
Template Strand
The strand copied to synthesise mRNA
What happens after TFIIH destabilises DNA?
TFIIF binds non-template strand, whilst template strand follows through polymerase active site three NT deep, bending sharply and then clamped for elongation
Elongation
This is the successive transcription of nucleotdies of the template strand from 5’s to 3’
Which end are nucleotides transcribed from?
3’ end.
How does trigger loop permit hydrogen bond formation in the polymerase?
Trigger loop containing histidine residue alternates between clamping sites, promoting electron flow coupled with phosphodiester bond formation.
What are the two trigger loop states?
One allows NTP to enter active centre, and a closed state holding NTP in the active centre
When during PS can a second roundo of transcription occur?
After about 50-60NT are expressed.
What are the processesing pathways primary transcript undergoes after formation?
7’methylguanosie cap addition
3’ polyadenylation
Splicing of introns
Why is 7’MG cap addition important?
It allows ribosomal recognition for syntheses?
What happens in 3’ adenylation?
The 3’ undergoes exonuclease digestion to a short sequence where a poly-a tail can be added.
Why is it important transcription and RNA processing are coupled?
The occurence of one regulates the next, limiting diffusion required for progression.
