Which of the following amino acids is a precursor for dopamine, epinephrine, and norepinephrine?

The amino acid that serves as a precursor for dopamine, epinephrine, and norepinephrine is tyrosine. Tyrosine is converted into L-DOPA through the action of the enzyme tyrosine hydroxylase, which is the rate-limiting step in the synthesis of catecholamines. L-DOPA is then further decarboxylated to dopamine. From dopamine, the synthesis continues with the addition of a hydroxyl group to form norepinephrine and then a methyl group to produce epinephrine. This metabolic pathway establishes tyrosine as the critical starting material for the production of these important neurotransmitters and hormones, all of which play significant roles in the nervous system and the fight-or-flight response.

Other amino acids listed do not participate in this specific pathway: arginine is involved in the production of nitric oxide; tryptophan is a precursor for serotonin; and glycine plays a role primarily as a simple neurotransmitter and in the synthesis of proteins, but does not contribute to the catecholamine pathway. Thus, tyrosine is definitively the correct answer due to its direct involvement in the biosynthesis of dopamine, norepinephrine, and epinephrine.