Fig. 1
From: DNA methylation, the early-life social environment and behavioral disorders
DNA methylation reactions. DNA methyltransferases transfer methyl groups (CH 3 ) from the methyl donor S-adenosyl-l-methionine to cytosines in DNA. Two kinds of DNA methylation reactions are shown; de novo methyltransferases (DNMT3a and DNMT3b) add new methyl groups to cytosines in DNA, maintenance DNA methyltransferase (DNMT1) copies the DNA methylation pattern from the template strand following DNA replication. Passive demethylation: if DNMT1 is absent during DNA replication, the DNA will be copied without being methylated and will be thus “passively” demethylated. DNA could be actively demethylated by demethylases that remove the methyl groups from DNA in the absence of DNA replication (see Fig. 2)