Serine is a nonessential amino acid that exists in two forms, or isomers: L-serine and D-serine. L-serine is synthesized from other amino acids, particularly glycine, or other protein metabolites. Serine plays important roles in the body, such as the synthesis of protein, fatty acid, DNA and RNA, brain and nervous system function, cellular proliferation, antibody production, muscle growth and metabolism. Serine also works to the benefit of other chemicals in the body as a precursor to the production of certain amino acids, other cell building blocks and lipids. Serine is commonly found in egg, soy, fish, seeds and other high protein options.