Which codon is selenocysteine?
UGA codon
Unlike other amino acids present in biological proteins, selenocysteine is not coded for directly in the genetic code. Instead, it is encoded in a special way by a UGA codon, which is normally the “opal” stop codon.
Is selenocysteine found in humans?
Selenocysteine, the 21st amino acid, has been found in 25 human selenoproteins and selenoenzymes important for fundamental cellular processes ranging from selenium homeostasis maintenance to the regulation of the overall metabolic rate.
What is selenocysteine tRNA?
Selenocysteine (Sec) tRNA([Ser])Sec donates Sec to protein, but interestingly, this amino acid is synthesized on tRNA which is first aminoacylated with serine. Thus, the identity elements in tRNA([Ser])Sec for aminoacylation correspond to elements for seryl-tRNA synthetase recognition.
Where is selenocysteine found?
Selenocysteine is located in the active sites of enzymes that participate in oxidation–reduction reactions. These include glutathione peroxidase, thioredoxin reductase, and iodothyronine deiodinase. The incorporation of selenocysteine into the growing peptide chain occurs by a unique suppressor tRNA and a stop codon.
What is selenocysteine insertion sequence?
In biology, the SECIS element (SECIS: selenocysteine insertion sequence) is an RNA element around 60 nucleotides in length that adopts a stem-loop structure. This structural motif (pattern of nucleotides) directs the cell to translate UGA codons as selenocysteines (UGA is normally a stop codon).
Who discovered selenocysteine?
Selenium is a micronutrient and an antioxidant in the form of selenocysteine. Selenium was fist discovered to be an essential trace element in the 1950s by the German scientist Klaus Schwarz.
How is selenocysteine formed?
Selenophosphate is synthesized from selenide and ATP by selenophosphate synthetase 2 (SPS2). Sec was the last protein amino acid in eukaryotes whose biosynthesis had not been established and the only known amino acid in eukaryotes whose biosynthesis occurs on its tRNA.
How is Pyrrolysine made?
Pyrrolysine is synthesized in vivo by joining two molecules of L-lysine. One molecule of lysine is first converted to (3R)-3-methyl-D-ornithine, which is then ligated to a second lysine. An NH2 group is eliminated, followed by cyclization and dehydration step to yield L-pyrrolysine.