103175.fig.002
Figure 2: Figure showing methylation of cytosine residues at CpG sites. The addition of a methyl group to convert the DNA base cytosine to 5-methylcytosine is catalyzed by DNA methyltransferase (DNMT). The methyl group is transferred from S-adenosylmethionine (SAM) to the 5-carbon position of cytosine.