What is special about methylated DNA

DNA methylation

The DNA methylation represents an important change in the structure of the DNA and thus also in its properties!

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DNA methylation is considered the most important epigenetic change!

Epigenetics = properties of the cell that are inherited by daughter cells -> are not encoded in the DNA sequence!

The DNA is chemically modified by methyl groups (-CH3) attach. These methyl groups are bound to the DNA by the enzyme methyl transferase. The DNA sequence is not changed by this methylation, but its properties are influenced!

The DNA methylation enables the cell to selectively use certain areas of DNA. DNA methylation represents a specific statement made by DNA, much as it does in text formatting.

The currently displayed webpage has highlighted important mnemonics in boxes - this would be e.g. B. "our" DNA methylation.

DNA methylation becomes Gene regulation used. Often there are sites in the area in front of a gene (= upstream, upstream) that show different methylation patterns compared to the surrounding sequences. These patterns determine the reading frequency of the underlying gene.

DNA methylation has a visible influence on gene expression. Methylated cytosines (promoter region of the gene) lead to an inactivation of this gene.

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Methylation of the promoter region = inactivation of gene expression!

Imprinting or genomic imprinting is also dependent on methylation patterns in the DNA. The transmission of genetic information through the germ line cells of the mother or father can be controlled by methylation. In this way, alleles of mother or father can be switched “active” or “inactive”. This "shutdown" of z. B. the paternal allele leads to gender-specific expression of phenotypic characteristics.

Example (see also hereditary diseases) is the inheritance of the Prader-Willi Syndrome or Angelman syndrome. So the mutation is identical; the question of whether the genetic information comes from the mother or the father is decisive for the pronounced phenotype.

In a healthy person, for example, the parts of the paternal allele are unmethylated (i.e. active), those of the maternal allele are methylated (thus inactive).

Shifts in this methylation pattern in the area of ​​chromosome 15 (15q11-13) lead to Prader-Willi syndrome: deletion of the paternal allele, a maternal deletion or imprinting defects. Result => Only the inactive maternal copy is read.

Angelman syndrome: Usually a deletion of the maternal allele or, in rare cases, a paternal UPD (unipaternal disomy) and an imprinting defect. Only the paternal copy can be read here.

Cancer cells also usually show altered methylation patterns when compared to "healthy cells".

In eukaryotes there are areas of DNA that are of particular importance for methylation. These are called CpG islands. The content of bases G and C is particularly high here.

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DNA methylations are interesting in connection with high school exams on the question of cancer - cell cycle - gene regulation.

Methylation and its effect on DNA and gene expression.