Final answer:
Amino acid neurotransmitters are not considered biogenic amines because biogenic amines lack a carboxyl group, altering their classification from amino acids. Amino acid neurotransmitters such as glutamate, GABA, and glycine have specific systems and effects, whereas biogenic amines have mixed effects and can influence more complex cellular processes.
Step-by-step explanation:
Amino acid neurotransmitters are not considered biogenic amines because while biogenic amines do contain an amine group, they no longer possess a carboxyl group and thus are not classified as amino acids anymore. Moreover, biogenic amines such as serotonin, dopamine, and others are created from amino acids through enzymatic processes but their structure is significantly altered during this transformation. On the other hand, neurotransmitters that are still considered amino acids — such as glutamate (Glu), gamma-aminobutyric acid (GABA), and glycine (Gly) — retain their amino group and their carboxyl group, which are typical of the amino acids used to make proteins.
Amino acid neurotransmitters have systems specific to them, like the glutamatergic, GABAergic, and glycinergic systems, and they are typically associated with only one primary effect — excitatory in the case of glutamate and inhibitory in the cases of GABA and glycine. This contrasts with biogenic amines, which can have mixed effects depending on the receptor types they interact with, such as D1 receptors being excitatory and D2 receptors being inhibitory. Furthermore, biogenic amines can influence other cellular processes that are not directly related to membrane potential changes, such as gene transcription and metabolic processes within neurons.