Аннотация:Selenocysteine (Sec), the 21st amino acid in the genetic code, is encoded by UGA. The pathway of Sec biosynthesis in eukaryotes has only recently been discovered. Sec is constructed on its tRNA that is initially aminoacylated with serine and modified to a phosphoseryl-tRNA intermediate with the help of several dedicated enzymes. More than 50 selenoprotein families are now known with most selenoproteins being oxidoreductases. Development of bioinformatics tools led to the identification of entire sets of selenoproteins in organisms, selenoproteomes, which in turn helped explain biological and biomedical effects of dietary selenium and identify new functions of selenium in biology. Roles of selenium and selenoproteins in health have also been addressed through sophisticated transgenic/knockout models that targeted removal or modulation of Sec tRNA expression.