methylated

Methylated is an adjective used in chemistry and biology to describe a molecule that bears one or more methyl groups, −CH3, attached to another atom or molecular fragment. The methyl group is derived from methane and is a common functional unit in organic synthesis and metabolism.

In organic chemistry, methylation is the process of adding a methyl group to a substrate. It changes properties such as lipophilicity and sterics and can alter reactivity. Common methylating agents include methyl iodide, dimethyl sulfate, and methyl triflate; reactions include N‑methylation, O‑methylation, and C‑methylation.

In biology, methylation most often refers to DNA methylation, the addition of a methyl group to cytosine residues by DNA methyltransferases. This epigenetic modification influences gene expression, development, genomic imprinting, and X chromosome inactivation. Abnormal methylation patterns are associated with aging, cancer, and other diseases. Proteins and RNA can also be methylated.

In everyday language, methylated spirits refers to denatured alcohol for solvent or fuel, typically containing methanol added to discourage drinking. Such mixtures are toxic and should be handled with care.

Environmental methylation includes microbial methylation of pollutants and metals, which can affect solubility and toxicity. A well-known example is methylmercury, produced by bacteria in anaerobic environments, a potent neurotoxin that bioaccumulates in aquatic food webs.