<prompt> Selenocysteine is derivative of which amino acid?CysteineAlanineArginineGlycine  <response>: Selenocysteine is the 21st amino acid.its biosynthesis is by replacing oxygen from serine by selenium.cysteine is formed from serine reversible. hence selenocysteine is formed from cysteineRef: DM Vasudevan - Textbook of Biochemistry, 7th edition, page no: 215 