Ask AI: Describe the molecular processes by which cytosines within the DNA molecule can undergo methylation and demethylation in somatic cells.

Methylation is a process in which a methyl group (CH3) is added to a DNA molecule, usually to a cytosine within a CpG dinucleotide (a sequence of two nucleotides, cytosine and guanine, in a DNA molecule). In somatic cells, DNA methylation is catalyzed by enzymes known as DNA methyltransferases, which add methyl groups to cytosines within the DNA molecule. Demethylation is a process in which methyl groups are removed from the DNA. In somatic cells, demethylation is catalyzed by enzymes known as Ten–Eleven Translocation (TET) enzymes, which oxidize methylated cytosines and convert them to hydroxymethylated ones. Finally, these hydroxymethylated cytosines are then converted to unmethylated cytosines by base excision repair (BER) pathways.