Q31. One of the following compounds is NOT a neurotransmitter
Answer: (C) Histidine
Histidine is not a neurotransmitter, while the others are established ones in the nervous system. This makes it the correct choice for the compound that does NOT function as a neurotransmitter.
Option Analysis
Dopamine
Dopamine acts as an excitatory neurotransmitter in brain pathways linked to reward, motivation, and motor control. It belongs to the catecholamine family and binds to specific receptors like D1 and D2.
Glutamic Acid
Glutamic acid, or glutamate, is the primary excitatory neurotransmitter in the vertebrate brain, responsible for over 90% of synaptic connections. It drives processes like learning and memory via ionotropic receptors such as NMDA and AMPA.
Histidine
Histidine serves as a precursor to histamine, which is a neurotransmitter involved in wakefulness and allergic responses. Histidine itself functions mainly as an essential amino acid in protein synthesis and enzyme catalysis, not direct neurotransmission.
Glycine
Glycine is a key inhibitory neurotransmitter in the spinal cord and brainstem. It opens chloride channels via glycine receptors, hyperpolarizing neurons to reduce excitability.
Neurotransmitters play a vital role in neural signaling, and questions like “one of the following compounds is NOT a neurotransmitter” test key concepts in biochemistry and neuroscience. This guide breaks down dopamine, glutamic acid, histidine, and glycine to identify the correct answer for exams such as GATE Life Sciences.
Neurotransmitter Basics
Neurotransmitters are chemicals released by neurons to transmit signals across synapses. Common types include amino acids like glutamic acid and glycine, plus monoamines like dopamine. Not all amino acids qualify—histidine, for instance, does not act directly as one.
Detailed Breakdown
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Dopamine: Key in reward circuits; derived from tyrosine.
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Glutamic Acid: Main excitatory agent; drives synaptic plasticity.
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Histidine: Amino acid precursor to histamine, but itself NOT a neurotransmitter.
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Glycine: Inhibitory in spinal pathways.
| Compound | Neurotransmitter Role | Type |
|---|---|---|
| Dopamine | Excitatory, reward/motor | Catecholamine |
| Glutamic Acid | Excitatory, learning/memory | Amino acid |
| Histidine | None (precursor only) | Amino acid |
| Glycine | Inhibitory, spinal inhibition | Amino acid |
For life sciences students, recognizing histidine as the one that is NOT a neurotransmitter sharpens exam prep. Glutamic acid’s role in over 90% of brain synapses underscores its importance.
