View source for KSH 0611 Review Epigenetic modifications regulate gene expression

<h1>&nbsp;Epigenetics</h1>

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<h2>Definition : Heritable changes in gene activity and expression that occur without alteration in DNA sequence</h2>

<h2>Different cells control switching on and off in different genes</h2>

<h2>Two well-known epigenetic modifications</h2>

<ul>
	<li>Chemical modification to the cytosine residues of DNA (DNA methylation)</li>
</ul>

<p><img src="http://www.ks.uiuc.edu/Research/methylation/dna_mdna.png" />(http://www.ks.uiuc.edu/Research/methylation/dna_mdna.png)</p>

<ul>
	<li>Histone modification</li>
</ul>

<h2>Why is it important ? &gt;&gt;&gt; Epigenetic&nbsp; modifications regulate gene activity and expression during development and differentiation, or in response to environmental stimuli</h2>

<h2>Epigenetics is considered a bridge between genotype and phenotype</h2>

<h2>Explain how cells carrying identical DNA differentiate into different cell types &gt;&gt;&gt; Epigenetics</h2>

<h2>Epigenome - global analyses of epigenetic markers across the entire genome</h2>

<h2>Chromatin - Histone protein / DNA complex&nbsp;in eukaryotic cells</h2>

<p>Basic Unit - nucleosome - 146 bp of DNA wrapped around an octamer of the four core histones (H2A, H2B, H3 and H4)</p>

<ol>
	<li>Euchromatin - transcriptionally active state - the region where DNA is accessible due to the relaxed state of nucleosome arrangement</li>
	<li>Heterochromatin - transcriptionally inactive state - the area where DNA is packed into highly condensed forms that are inaccessible to transcription factors</li>
</ol>

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<h2>How to regulate Protein Synthesis - Epigenetic inheritance controls the amount of the transcribed mRNA. Thus, protein production is regulated.</h2>

<h4>Ex) Alcohol dehydrogenase (ADH) breaks down alcohol in liver cells.</h4>

<h4>We could increase the mRNA of <em>ADH</em>&nbsp; and then make ADH more than usual when we drink much&nbsp;</h4>

<h2>Only 2 % of human genome encodes protein and the other 98% controls gene expression by epigenetic mechanism.</h2>

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