<prompt> Which among the following amino acid is heterocyclic in structure?HistidinePhenylalanineHydroxyprolineProline  <response>: Histidine and tryptophan are heterocyclic amino acids. Phenylalanine and tyrosine are aromatic amino acids. Proline is an imino acid. Hydroxyproline, hydroxylysine, and ornithine are derived amino acids. Ref: Textbook of Biochemistry for Medical Students By Dm Vasudevan, 2010, Page 20. 