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Module 5: Gene expression in eukaryotes
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Detailed lecture notes on module 5 which is about gene expression in eukaryotes.
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Lecture 1 transcriptional regulation in Eukaryoteschromatin structure
EukaryoticDNA is highly organized into chromatin
twotypes of chromatin heterochromatin and euchromatin less condensed andtranscriptionallyactive
Even in euchromatin there are problems with getting access to Dna
Dna hypersensitivity and gene activation
Experimentdone on reticulocytes immature blood cells
two tissues one expressing gene or interest and one not expressing gene or interest
chromatin in these cells had their Dna extracted and was partially digested by Dnaase
partial digestion means that Dnaase wasthere justlongenough to nick Dna in a few places
immature not mature expressing
expressingglobin globin thefact that there is one band in nonglobin
y y gene tissue and two in the tissue that has globin
gene expressed shows that during this transition
from transcriptional inactivity to transcriptional
activity chromatin had changed in structure
where globin genes have beenactivated
Dnaase is able to cutDna more easily and
chops Dna in a different place
as genebecomestranscriptionally
active chromatin proteins are
moved out of the way
Histone structure
Nucleosomes are made up of a set of histone proteins
histone proteins are all very similar in structure
they consist of a globular domain and armswhich are positively charged as they containamino acids
amino acids such as lysine and arginine charged
globular domains are in the centre having Dna around
arms stick out through Dna and interact with it through electrostatic attractions
Interactions with Dna is mostly non specific and needs to be modified during transcriptional
activation
, Histones are veryhighly modified in different ways and this alters their activity
replacing a positive charge with a negative
one and histone is interacting with negcharged
ace
Dna it is going to loosen association between
histones and Dna
enhancer acts as set or binding sites for
sequence specific transcription factors
sequence specific factors can be brokendown into
distinct functional domains meaning theyneed a
di domain as well as one that
rest of the transcription
recognizes polymerase and
functional distinction
apparatus transcription activation domain
frompromoters
recognizessequence or Dna
transcriptional stimulation in Eukaryotes
linear diagram showing a promoter sequence
with Rnapolymerase and general transcriptionfactors
Further upstream is the enhancer sequence with
a set of transcription Factors
these proteins operatetogether to mediate
transcriptional activation
oncegeneral transcription factor proteins have binded to Dna they recruit furtherproteins
one is the mediatorcomplex which is a complex or so proteins which are associated with Rna
polymerase and is important for activating transcription and moving chromatin
Atp dependentchromatin modification proteins also move and displace chromatin and are
recruited by rna polymerase and general transcription factors and stimulated by sequence specific
factors
adaptor proteins bridge gaps between sequence specific factors and promoter boundproteins
Histone acetylase chat that interact with sequence specific transcription factors and once
recruited they start acetylating histones around site or transcription
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