Serine amino acid. Polarized light micrograph of crystals of serine, one of the 20 amino acids used to form proteins. This is the naturally-occurring L-stereoisomer known as L-serine. It is critical for the synthesis of the body's proteins and enzymes, and necessary for specific functions in the central nervous system, as well as the proper metabolism of fats, fatty acids, cell membranes, and muscle growth. Altered levels are linked to disorders such as fibromyalgia, chronic fatigue syndrome, depression, insomnia, confusion and anxiety. It is also used in cosmetic products as a natural moisturising agent. Field of view size: 1.485 x 2.227 millimetres.