Polarized light micrograph of cysteine amino acid single crystals and aggregate crystals. Cysteine is a semi-essential amino acid that is oxidized to form cystine. The amino acids are the essential building blocks of all proteins. Cysteine may be essential for infants, the elderly and individuals with certain metabolic diseases or who suffer from malabsorption syndromes. It is a precursor in the food technology, nutritional supplements (E920), fertilizers, pharmaceutical, biodegradable plastics and personal care industries. It is used as an additive in cigarettes, acting as an expectorant and increasing the beneficial antioxidant glutathione. It also reduces the negative effects of alcohol. Field of view size: 1.49 x 2.23 mm (0.059 x 0.088 in)