DNA modifications/RNA polymerase II/ Transcription Flashcards
Chromatin structure is controlled through (2)
- Histone Modifications
2. DNA Methylation
Types of histone modifications (3)
- Phosphorylation
- Methylation
- Acetylation
Modifications to histones determine
how tightly the DNA is coiled.
Methylation closes DNA
Acetylation opens DNA
Histone acetylation leads to
uncoiling of chromatin
When chromatin modifications are inherited it is called
epigenetics
DNA is usually methylated at
cytosine residues next to guanine
‘Cpg islands’
DNA methylation usually
silences a gene
‘turns off’
DNA methylation enzyme
Methyl transferase
DNA methylation silences genes in two ways:
- Physically hinder
the binding of TFs - Transcriptionally silence with MBDs
methyl Cpg binding domain proteins: recruit proteins to modify the histones to form dense heterochromatin (inactive)
Different chromosomes occupy different
‘territories’ in the nucleus
influences gene expression through co localisation of nuclear machinery
RNA polymerase II structure (5)
- has 12 subunits
- has a CTD which carries splicing machinery
- contains transcription factors
- cannot correct mistakes
- contains Mg2+ or Mn2+
Transcription is regulated by transcription factors that bind to
promotor or enhancer sequences
Core promotor sequences (5)
- GC box
- CAAT box
- BRE box
- TATA box
- Initiator
RNA polymerase II contains
transcription factors TFIIB, D,E,F,H
which bind to promotor sequences or initiate transcription
TFIID binds to the
TATA box
initiates recruitment of other factors and regulates binding of TBP (tata binding protein TF)
TFIIB binds to the
BRE box
positions RNA pol II at initiator site
TFIIF stabilises
interaction between TBP (tata binding protein, a TF) and TFIIB
TFIIE attracts
TFIIH
Mutations in the TFII complex cause (2)
- DNA repair disorders Xeroderma pigmentosum (skin cancers)
- Premature ageing syndromes
Cockayne’s syndrome
DNA enhancers recruit
- other proteins that cause DNA looping
- bring mediator proteins into contact with transcription machinery
- are distant from gene (to make loop)
- function in either direction
DNA insulators are a segment of DNA that acts as
a boundary between 2 genes
can silence a gene
- regulate enhancers
- regulate multiple genes
- can act as chromatin boundary markers
