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Lecture 3

BIOL 4061 Lecture Notes - Lecture 3: Post-Translational Modification, Histone Code, Nucleosome


Department
Biology
Course Code
BIOL 4061
Professor
John C. McDermott
Lecture
3

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Jan 21st
We will talk about the histone code hypothesis,
The central component of chromatin structure, the physiological template for gene expression =
nucleosome.
We have between the signal transcriptional factor and the transcriptional regulators (?), and the third
factor is how the chromosome packaging of the genome is regulated to provide access to the
transcriptional regulatory proteins.
Classically, epigenetics is referred to heritable traits that are not linked to the changes in the DNA
sequence (Epi = above, above the genetics) modification or the regulation of the genome for the things
that do’t alte the pia DNA seuee.
General solenoid structure of the chromatin, unravel it and the nucleosomes look like beads on a string
where the octameric core is in the center with DNA wrapped around it and histone tails sticking out
prominently. Anything that alters the charge of the positively charged histone tails, affects the
condensation of the chromatin. The core consists of 2 subunits : H2A, H2B, H3 and H4. Histone 1
assoiates ith the like egio etee the uleosoes ad it’s ot eall a pat of the uleosoe.
In general methylation of the histone tails is a characteristic feature of the heterochromatin (condensed
protein), and the reduction of the charge of the histone tails by acetylation results in relaxing the
uleosoe stutue → taslatioal atiatio.
Histone code hypothesis by David Allis.
The reader and writer and the eraser in terms of controlling the nucleosome structure. It’s a good
analogy. The writer proteins write certain messages on histones (post translationally modify histones by
acetylation or methylation), the readers are proteins that see that signal (message) and they help effect
the change. Epigenetics is heritable and reversible. Is not a change to the primary DNA sequence and is a
post translational modification. The eraser removes the signals.
The 2 aos goig eithe a allo ou to eese gee epessio, Repessed state → gee off, ad
deepessed → gee is on. These states are interconvertible.
The readers are proteins with particular domains that recognize the post translationally modified
histones and fall into the class of the Bromo (region within a larger protein, it can bind to the acetylated
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