<prompt> Amino-acid substitute for tryptophan without altering proteins characteristics ?TyrosinePhenylalanineMethionineAlanine  <response>: Ans. is b i.e., Phenylalanine Tryptophan is an aromatic amino acid, thus it can only be replaced with other aromatic amino acid.Other two aromatic amino acids are :?PhenylalanineTyrosineAmong 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 substitude for tryptophan is phenylalanine. Tyrosine cannot substitute since it has hydrophilic propey 