Methylation (IMAGE) Max-Planck-Gesellschaft Caption Special enzymes transfer methyl groups to the cytosine building blocks of DNA. A methyl group consists of one carbon atom combined with three associated atoms of hydrogen (CH3). Credit Environmental Health Perspectives, 2006 Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.