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  • Easiest Epigenetic mechanism to study using the technology we currently have

  • Definition: The addition or removal of a Methyl group (CH3) to the cytosine (C from A-T-G-C) site in DNA. 

  • The addition of this Methyl group represses transcription of the site where it's located.

  • A gene with a Methyl group is a silenced gene.  (Citation-3)

 

How does this affect us?

Each and every one of our cells have the same genetic material. For example, cells from our skin, mouth, or heart are genetically identical and contain the entire makeup of the human genome. The difference between them is that each gene that a tissue doesn't need is turned off through the use of DNA Methylation. (Citation-1)

  • Changes in some Methylation patterns are called epimutations.

  • Epimutations result in a differently expressed gene

  • Epimutations may even lead to cancer if the genes that play a role in our defense against it is inactivated.(Citation-3)


If you were to take one cell from the human body and unravel its DNA, the DNA would measure approximately 2 meters long from end to end. The remarkable thing is, these 2 meters of genetic material must fit into a nucleus which is only 6 μm (about  0.000236 inches) in diameter. (Citation-17) This extraordinary feat called DNA packaging is equivalent to packing 40 km (24 miles) of extremely fine thread into a tennis ball. (Citation-10)

Histones

  • Proteins that act as spools upon which DNA wraps around

  • Responsible for the first and most basic level of chromosome organization: the nucleosome (Citation-10)

  • Play a pivotal role in transcription factors depending on how tight or loose the DNA is wound around it



 

 

 

(A) Packed and condensed nucleosomes under electron microscope

(B) Unpacked and decondensed nucleosomes under electron microscope

(Citation-NucleosomesNCBI)

 

 

  • The number of Acetyl Groups on the histones determine how tight or loose the DNA is wrapped (Citation-1)
  • The more Acetyl Groups there are, the looser the DNA
  • The less Acetyl Groups there are, the tighter the DNA

 

 

 

 

  • Histone deacetylases (HDACs) are enzymes that are responsible for removing abnormal amounts of acetyl groups. (Citation-11)

  • The removal of an acetyl group is called deacetylation

    • Abnormally high levels of HDAC enzymes result in uncontrollable histone deacetylation

    • The removal of  acetyl groups from a histone will result in the DNA wrapping tighter and tighter until the DNA is too tightly wound to be transcribed. The gene on the tightened DNA is "silenced," or is not expressed. (Citation-12)

     
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