<prompt> Amino-acid substitute for tryptophan without altering proteins characteristics -TyrosinePhenylalanineMethionineAlanine  <response>: Ans. is b i.e., Phenylalanine o Tryptophan is an aromatic amino acid, thus it can only be replaced with other aromatic amino acid, o Other two aromatic amino acids areaPhenylalaninebTyrosineo Among these two, phenylalanine can substitute tryptophan but not tyrosine becausePhenylalanine and tryptophan both are hydrophobic non-polar.Whereas, tyrosine is hydrophilic Polar.The only other aromatic residue that can substitute for tryptophan is phenylalanine. Tyrosine cannot substitute since it has hydrophilic property 