| Function | Amino acid | Additional information |
| Predominant circulating amino acid with the SMALLER molecular mass, used in amino group transport | |
| Precursor to the neurotransmitter serotonin | |
| Directly INCORPORATED during de novo synthesis of purines | |
| Conjugated to a cholesterol derivative to form a bile salt | |
| Form of activated ammonium ions, source of ammonium in the kidney | |
| Precursor to the vitamin niacin | |
| Reacts with ATP to form SAM, an important source of methyl groups for methylation reactions | |
| Predominant circulating amino acid with the LARGER molecular mass, used in amino group transport | |
| Amino acid neurotransmitter with the LARGER molecular mass - primary excitatory neurotransmitter in the CNS | |
| Reactant in ammonia fixation | |
| Yields intermediate in polyamine biosynthesis, which are important for binding to excessive negative charge | |
| Condenses with succinyl CoA in the first step of heme biosynthesis | |
| Amino acid neurotransmitter with the SMALLER molecular mass | |
| Source of amino groups in transamination reactions | |