DNA methylation is carried out by enzymes called DNA methyltransferases (DNMTs). These enzymes add a methyl group to the fifth carbon atom of the cytosine base within DNA, resulting in the formation of 5-methylcytosine (5mC). They accomplish this process by utilizing S-adenosyl methionine (SAM) as a methyl donor. DNMT1 carries out DNA methylation maintenance post-replication, quickly methylating the newly formed DNA strand to match its template. In somatic cells, over 98% of DNA methylation occurs specifically at CpG dinucleotides.