What Is the Purpose of DNA Methylation?

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  • Written By: Mark Wollacott
  • Edited By: Lauren Fritsky
  • Last Modified Date: 14 November 2019
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The purpose of deoxyribonucleic acid or DNA methylation is to alter how genes are expressed within an organism. Methylating DNA is integral to the development of complicated and higher level organisms, but is also used by both eukaryotic and prokaryotic cells. The most important function is to allow the actions of different cells to be differentiated from one another.

DNA is a chain of nucleic acids contained within the nucleus of a eukaryotic cell and loose within a prokaryotic cell. It consists of two long polymer chains containing a specific sequence of amino acids. The sequence used by the cell is a blueprint of the cell’s genetic make-up. The genetic coding determines the construction and function of all cells.

DNA methylation is a process involving the addition of a methyl group to the DNA chain. This methyl group is a hydrocarbon group usually found in organic compounds. It arrives in three highly-reactive forms: anions, cations and radicals. The three forms are hard for scientists to detect because being highly-reactive means they are rarely found as an isolated entity.


In mammals, DNA methylation takes place when the methyl group attaches itself to one of two locations. The first location is the fifth carbon on the cytosine pyrimidine ring. The second location is the sixth nitrogen of the adenine purine ring. Any modifications methylation makes to DNA like this are inherited during cell division. Cell division occurs when one cell copies its data, then divides into two equal new cells.

The purpose of DNA methylation in mammals and many other animals is to ensure normal development. This includes phenomena such as genome imprinting and x-chromosome inactivation. The majority of the process takes place during fetal development.

Plants have a total of three methylation points in the cytosine area. Many of the effects of methylation are similar between plants and mammals. Fungi, on the other hand, tend to have more variation. The amount of methylation taking place within developing fungi depends on the species involved. Brewer’s yeast, for example, has a very low amount of methylation.

Abnormal DNA methylation is the chief cause of cancer cell development. This occurs when the addition of a methyl group to the DNA causes a mis-programming of the genomes. Such abnormal imprinting can also be the cause of inherited diseases and conditions.

There are several scientific methods for detecting DNA methylation. These methods include whole genome bisulfite sequencing and assays such as HELP, which stands for HpaII tiny fragment Enrichment by Ligation-mediated PCR, and ChIP-on-chip. Scientists can also use restriction landmark genomic scanning, but this is a difficult and complex process and is used rarely as a result.


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