Which is 21st amino acid-

Ans. is 'd' i.e.t Seleno cysteine Amino acido Amino acid are basic structural unit of protein,o Amino acid arePrimary (standard) amino acidsModified amino acidsPrimary (standard) amino acidso In human body, 20 amino acid are involved in formation of all proteins,o These are called standard amino acids.Nutritionally EssentialNutritionally NonessentialArginineAlanineHistidineAsparagineIsoleucineAspartateLeucineCysteineLysineGlutamateMethionineGlutaminePhenylalanineGlycineThreonineProlineTryptophanSerineValineTyrosineModified or nonstandard amino acido In addition to standard (primary) amino acids, a small number of modified amino acids are found in proteins. These amino acids are formed by the modification of one of the 20 standard amino acids.Cystine : - It is formed by linkage of two cysteine through a disulfide bond.Hydroxyproline and hydroxy lysine: - Hydroxylation of proline and lysine occurs in formation of collagen.Desmosine and isodesmosine : - These are formed by the oxidation and crosslinking offour lysine side chains. These are found in elastin.Selenocysteine : - This is considered to be 21st standard amino acidQ. It is present at the active site of several human enzymes, e.g., glutathione peroxidase, deiodinase, glycine reductase. Selenocysteine has a structure similar to cysteine, but containing the trace element selenium in place of sulfur atom of cysteine.