selenocysteine

(noun)

A naturally-occurring amino acid, present in several enzymes, whose structure is that of cysteine but with the sulfur atom replaced by one of selenium.

Related Terms

Examples of selenocysteine in the following topics:

  • Amino Acid Synthesis

    • Selenocysteine and pyrrolysine are not encoded by the universal genetic code.
    • The remaining two, selenocysteine and pyrrolysine, are incorporated into proteins by unique synthetic mechanisms.
    • Selenocysteine is incorporated when the mRNA being translated includes a SECIS element, which causes the UGA codon to encode selenocysteine instead of a stop codon.

  • The Central Dogma: DNA Encodes RNA and RNA Encodes Protein

    • The stop codon UGA is sometimes used to encode a 21st amino acid called selenocysteine (Sec), but only if the mRNA additionally contains a specific sequence of nucleotides called a selenocysteine insertion sequence (SECIS).

  • Amino Acids

    • The 21st amino acid, not shown here, is selenocysteine, with an R group of -CH2-SeH.

  • The Protein Synthesis Machinery

    • Of the three termination codons, one (UGA) can also be used to encode the 21st amino acid, selenocysteine, but only if the mRNA contains a specific sequence of nucleotides known as a SECIS sequence.