Transcription and Splicing Flashcards
First step of gene expression
transcription = taking DNA and making it into RNA
What enzyme is responsible for transcribing genes
RNA Polymerase at the active site
Mechanism of RNA Polymerase
- separates two DNA strands in a transient bubble (12-14 bp, length of RNA-DNA hybrid within it is ~8-9 bp)
- uses one strand running 3’-5’ as a template to direct synthesis of a complementary sequence of RNA running 5’-3’
What are the three domains of life
Bacterial, Archaeal and Eukaryotic
What is meant by the statement “Transcription in eukaryotes is pervasive”
- genome is being transcribed abundantly
- a substantial portion of non-coding DNA sequences with important biological functions are transcribed into RNA molecules
- 12% of genes are transcription factors that regulate gene expression and transcribe themselves (chicken and egg)
What initiates transcription in eukaryotes
many proteins and complex cis-regulatory elements
What genes does RNA Polymerase I transcribe
5.8S, 18S, 28S rRNA genes
What genes does RNA Polymerase II transcribe
all protein-coding genes, plus snoRNA genes, miRNA genes, siRNA genes, IncRNA genes, and most snRNA genes
What genes does RNA Polymerase III transcribe
tRNA genes, 5S rRNA genes, some snRNA genes, and genes for other small RNAs
Why does RNA Polymerase II require a set of general transcription factors
RNA Polymerase II binds non-specifically and cannot recognize a gene promoter, so needs to be actively recruited to initiate transcription
Which transcription factor recognises the promoter
TF2B -> able to recruit RNA Polymerase in conjunction with TF2F
Role of core promoter sequence
- defines where transcription begins
- interact with RNAP II GTFs
- basal levels of transcription initiation
- located immediately upstream (5’) of the transcription start site
- fixed direction/orientation relative to gene
- unsymmetrical
TF2D composition
TBP and ~11 additional subunits called TAFs; C-terminal domain
Rold of TBP subunit (1)
recognises TATA box
Role of TAF subunits (~11)
- recognise BRE element in promoters
- recognise other DNA sequences near the transcription start point
- regulates DNA-binding by TBP
Role of TF2B subunit (1)
- recognises BRE element in promoters
- accurately positions RNA polymerase at start site of transcription
Role of TF2B subunits (3)
- stabilises RNA polymerase interaction with TBP and TFIIB
- helps attract TFIIE and TFIIH
Role of TFIIE subunit (2)
- attracts and regulates TFIIH
- stabilises open complex and allows for RNA synthesis
Role of TFIIH subunits (9)
- unwinds DNA at transcription start site
- phosphorylates Ser5 of the RNA polymerase CTD
- releases DNA polymerase from promoter
What is mRNA processing
capping, splicing, and 3’ end formation are associated with CTD of Pol II
What is DNA damage repair
DNA helicase subunits of TF2H have a role in nucleotide excision repair; transcription-coupled repair
Nuclear architecture
nuclear matrix, chromosomal domains; transcription foci in the nucleus; eu- vs. heterochromatin
DNA replication
transcription factor binding sites near origins of replication; actively transcribed genes are replicated in early S phase
How are S values related to rRNA name
- S value refers to rate of sedimentation in an ultracentrifuge
- larger S value = larger rRNA
