Methylation is a biochemical process which takes place continuously in every cell of the body. It is not one reaction but over one hundred reactions that occur in every cell of the body all the time. Imagine methylation cycles as wheel spinning with the help of methyl groups to drive the cycles. These methyl groups are being transferred (donated) from one chemical to another. Each of the cycles you see in this picture has a specific function which can be performed by methyl groups.