Registered Dietitian Domain 1 Practice Exam 2025 – Complete Prep Guide

Tryptophan is an essential amino acid that plays a critical role in the synthesis of various important biomolecules in the body. The correct option here is serotonin, which is a neurotransmitter derived directly from tryptophan.

The conversion process begins with tryptophan being hydroxylated to form 5-hydroxytryptophan (5-HTP), and then decarboxylation of 5-HTP leads to the production of serotonin. This pathway is significant as serotonin is involved in regulating mood, sleep, and appetite, among other functions.

In contrast, the other substances listed, such as catecholamines, phenylalanine, and tyrosine, are related to different metabolic pathways that do not involve tryptophan directly. Catecholamines (like dopamine, norepinephrine, and epinephrine) are derived from the amino acid tyrosine, which itself comes from phenylalanine. Tryptophan does not convert into either phenylalanine or tyrosine, making serotonin the correct substance formed from tryptophan.