DNA methylation is the biological process by which a methyl group, which is an organic functional group with the formula CH3, is added to DNA nucleotide. DNA, or deoxyribonucleic acid, is an important nucleic acid that stores the genetic information for any given organism. It is made up of four different molecules known as nucleotides; these are referred to as adenine, cytosine, guanine, and thymine. Through DNA methylation, a methyl group can be attached to a carbon atom on cytosine or to a nitrogen atom on adenine. The addition of a methyl group to these nucleotides can serve many important biological purposes, such as suppressing potentially harmful viral genetic information that is present in the human genome.
The DNA in many different types of organisms can undergo DNA methylation, though it does not always necessarily serve the same function. In plants, for example, scientists believe that methylation occurs to deactivate genes that could otherwise cause harmful mutations. In fungi, this process is used to moderate and control the expression of certain genes based on the particular conditions affecting the fungus. Methylation in mammals similarly moderates and inhibits the expression of certain genes; additionally, it is involved in the production of chromatin, a protein-DNA complex that makes up the structure of chromosomes.
Various enzymes, or proteins that catalyze biochemical reactions, are required in order to attach a methyl group to DNA nucleotides. The specific family of enzymes necessary for DNA methylation is known as DNA methyltransferase. DNA methylation tends to follow a pattern; once a nucleotide is methylated, copies of that nucleotide will also be methylated after DNA replication that occurs normally over the course of cell division. De novo methyltransferases are responsible for the initial methylation that occurs during early development. Maintenance methyltransferases add methyl groups to nucleotides that are produced through DNA replication; they ensure that copies of methylated DNA are also methylated.
Scientists use many different methods to detect DNA methylation in samples of DNA. Such methods can be used to determine the methylation of a given strand of DNA and to determine which specific genes are affected by methylation. The two main goals of the various DNA methylation analysis techniques are profiling and typing. Profiling is aimed at characterizing the methylation of an entire genome or similarly large genetic sample. Typing is aimed at examining the methylation of a few genes or DNA segments over many samples to ensure accuracy and to detect differences in different samples.
