Describe how H3Lys9me heterochromatin is formed - answer✔✔H3Lys9me heterochromatin
formation: Lys9 deacetylated by HDAC. Suvar39 then methylates lys9. Methylated lys9 is
recognised by HP1 and then HP1 binds. HP1 has chromodomain - chromodomains often
recognise and bind to methylated lys residues. Chromodomain on HP1 is specific for H3Lys9me
(with di or tri methylated lys 9). Binding of HP1 is thought to compact nucleosome arrays as
HP1s join together.
What is gene expression? - answer✔✔Process by which DNA is decoded to proteins
Causes protein synthesis (DNA to RNA by transcription, RNA to protein by translation)
It is highly regulated
What is transcription? - answer✔✔ds DNA to ss mRNA
Template strand copied 5' to 3'
Describe transcription in prokaryotes - answer✔✔RNA polymerase with sigma factor 70
(holoenzyme) makes contact with -35 and -10 promoter region (upstream from transcription start
site). This forms closed complex.
The DNA is opened (open complex) over transcription start site and RNA pol uses template
strand to begin making copy (initiation). Sigma factor 70 is released and the mRNA strand is
elongated 5' to 3'.
What does a promoter do? - answer✔✔Initiate and control transcription when RNA pol binds
What are +1, -10 and -35 sequences on prokaryote promoter? - answer✔✔+ 1 is the first base
that is used as template
-10 and -35 are consensus sequences which are strongest promoters and are upstream. Both
hexamers
Describe eukaryotic promoters (go into detail on core and regulatory regions) - answer✔✔There
is a core (basal region) around transcription start site, and a regulatory region upstream.
TATA box at -30 and initiator at +1 are found on the core region. There is also DPE at +30 and
BRE at -35. Often core regions will not have all of these elements
Regulatory region has proximal elements (UAS and URS) and distal (enhancer and silencer).
UAS and enhancer and activator binding sites which increases transcription. URS and silencer
are repressor binding sites which decrease transcription.
Sequences are less defined than they are in prokaryotes
What are CpG islands? - answer✔✔Regions with high frequency of CG sequences (CpG
islands). These CG sequences have C residues that are hypomethylated which causes decreased
transcription (due to less initiation)
What do reporter genes do? - answer✔✔Encode proteins whose levels can be easily measured eg
GFP and LacZ
Amount of reporter protein is proportional to gene expression (activity)
Reporter genes can be added to plasmids which cause recipient cells to have reporter gene
expression
Contrast types of RNA pol in prokaryotes and eukaryotes - answer✔✔In prokaryotes there's only
one
In eukaryotes there are at least 3 main ones
Similar structure but bacterial has 2 alpha, 1 beta, 1 beta prime and one omega subunit. Yeast
RNA pol II has 12 subunits.
What are types of RNA pol in eukaryotes? - answer✔✔RNA pol I - transcribe rRNA (28S, 18S
and 5.8S). Found in nucleolus
RNA pol II - transcribes mRNA (and snRNA and miRNA). Found in nucleus
RNA pol III - transcribes tRNA (and 5S, U6 and 7S RNA). Found in nucleus
RNA POL II IS THE MAIN ONE
What are general transcription factors (GTFs)? - answer✔✔TFII A,B,D,E,F and H
All but TFIIB are made complexes made of multiple polypeptides.
They are all specific to RNA pol II and form a complex on TATA box and recruit RNA pol II to
promoter and direct initiation and start site
Used at every promoter
Explain how PIC (Pre initiation complex) is assembled - answer✔✔TFIID binds to TATA box,
then TFIIA and subsequently TFIIB (TFIIB is recruited by D) join. TFIIB acts as a signal to
allow RNA pol II to bind. RNA pol II binds and is associated with TFIIF which therefore also
binds. TFIIE and TFIIH then join.
TFIIH has helicase activity that is powered by ATP hydrolysis. This separates template strand at
start site which forms open complex.
RNA pol II can now start transcription. As this begins RNA pol II is phosphorylated (a lot) on
the C terminal domain (CTD) (which is found on the end of the beta prime subunit)
TFIID and A may stay behind. B, E and H are released. F moves with RNA pol II along template
Describe TFIIH - answer✔✔Has 9-10 subunits
Has 2 parts: CORE and CAK
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