Phenylalanine is required for the production of many of your proteins, but none of your cells are capable of synthesizing this amino acid. what type of metabolic pathway must be responsible for providing this essential amino acid to your cells?

phenylalanine uses the bio synthetic pathway. It uses the same active transport channel as tryptophan to cross the blood–brain barrier in order to provide amino acid to the cell.

b. lithosphere, asthenosphere, mesosphere   is the answer most likely

the three components of a nucleotide are the nitrogenous base, the phosphate group and the five-carbon sugar.