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Hi friends, this is a very short video on difference between DNA methylation and histone
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acetylation. Both are epigenetic changes. Epigenetic changes are changes or modifications that influence gene expression without changing the DNA sequence. So there is no change in DNA
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sequence but gene expression is either turned on or turned off by means of epigenetic changes
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Classical examples include DNA methylation and histone acetylation. Now let us see the
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difference. DNA methylation as the word suggests it is a methylation of DNA. Methyl group is added
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to the DNA to the cytosine residues. So this is DNA to the cytosine residue as you see here
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methyl group is added. Exactly this is happening. At the fifth carbon position
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methyl group is added. It becomes 5-methyl cytosine. The enzyme involved is DNA methyl
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transferase whereas histone acetylation is the acetylation or addition of acetyl groups
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to the lysine residues of the histones. Histones are proteins on which the DNA is wrapped around
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You can see this is the histone, histone octamer to which the DNA is wrapped around. So acetyl
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group is added to the lysine residue of histone protein. The enzyme involved is histone acetyl
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transferase. By means of DNA methylation, chromatin condensation happens so that transcription factors
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may not have access to the promoter side thus gene expression is suppressed or genes are switched off
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by means of DNA methylation whereas histone acetylation causes relaxation of chromatin
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so that transcription factors can bind to the promoter region easily thus enhances gene expression
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or genes are turned on by means of histone acetylation. DNA methylation is a semi-reversible
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process that means demethylation. To remove this methyl group, it is an active process
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Classical example is X chromosome inactivation. During embryonic development in females, as you know there are two X chromosomes. One of the X chromosomes is inactivated primarily by
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means of DNA methylation whereas histone acetylation is a reversible process where
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acetyl groups are added or removed dynamically. So histone acetylation causes relaxation of the
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chromatin leading to gene expression or genes are turned on. Examples include acetylation of K9 and
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K27 on histone H3 is associated with enhancers and promoters of active genes and finally let me
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summarize these two. Demethylation of DNA actually causes nucleosomes to pack together so that
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transcription factors as you see cannot bind to the site or the promoter so that gene expression
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is turned off whereas by means of histone acetylation that results in relaxation of the
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chromatin so that transcription factors can bind and causes gene expression or genes are turned on
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Hope you are clear with the difference between DNA methylation and histone acetylation
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Take care, stay blessed. Thank you so much. You are with biologyexams4u.com
