Answer:
Alanine
Arginine
Asparagine
Aspartic Acid
Cysteine
Glutamic acid
Glutamine
Glycine
Histidine
Isoleucine
Leucine
Lysine
Methionine
Phenylalanine
Proline
Serine
Threonine
Tryptophan
Tyrosine
Valine
Selenocysteine
Pyrrolysine (not used in human protein synthesis)
Of these 20 amino acids, nine amino acids are essential: