page_title: Transcriptional regulation
section_title: At the level of cytosine methylation
hierarchical_section_title: Transcriptional regulation / In eukaryotes / At the level of cytosine methylation
caption_attribution_description: English: DNA methylation
context_page_description: In molecular biology and genetics, transcriptional regulation is the means by which a cell regulates the conversion of DNA to RNA, thereby orchestrating gene activity. A single gene can be regulated in a range of ways, from altering the number of copies of RNA that are transcribed, to the temporal control of when the gene is transcribed. This control allows the cell or organism to respond to a variety of intra- and extracellular signals and thus mount a response. Some examples of this include producing the mRNA that encode enzymes to adapt to a change in a food source, producing the gene products involved in cell cycle specific activities, and producing the gene products responsible for cellular differentiation in multicellular eukaryotes, as studied in evolutionary developmental biology.
  The regulation of transcription is a vital process in all living organisms. It is orchestrated by transcription factors and other proteins working in concert to finely tune the amount of RNA being produced through a variety of mechanisms.
context_section_description: 5-Methylcytosine is a methylated form of the DNA base cytosine (C) that regulates gene transcription in mammals.  Methylated cytosines primarily occur in dinucleotide sequences where cytosine is followed by a guanine, a CpG site.  The total number of CpG sites in the human genome is approximately 28 million. and generally about 70% of all CpG sites have a methylated cytosine.  Methylation of CpGs in a promoter region of a gene represses transcription while methylation of CpGs in the body of a gene increases expression.  TET enzymes play a central role in demethylation of methylated cytosines.  Demethylation of CpGs in a gene promoter by TET enzyme activity increases transcription of the gene.
caption: DNA methylation is the addition of a methyl group to the DNA that happens at cytosine. The image shows a cytosine single ring base and a methyl group added on to the 5 carbon. In mammals, DNA methylation occurs almost exclusively at a cytosine that is followed by a guanine.
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