Cysteine can be synthesized through multiple biochemical pathways: from serine via O-acetylserine intermediate (with sulfur donated as hydrogen sulfide), from reductive cleavage of the disulfide bond in cystine (using electrons from NADH), and from reduction of the oxidized form cysteic acid. A related rare amino acid, selenocysteine, is synthesized not from free cysteine but by chemical modification of serine after it has been charged onto a specialized non-canonical transfer RNA, and is incorporated into proteins via recoding of a stop codon. This topic belongs to amino acid biochemistry, specifically sulfur-containing amino acid metabolism, and connects to genetic disease when the related transsulfuration pathway (homocysteine to cysteine) is disrupted.
Cysteine can be synthesized through multiple biochemical pathways: from serine via O-acetylserine intermediate (with sulfur donated as hydrogen sulfide), from reductive cleavage of the disulfide bond…