Which one of the following statements about ligand-gated ion channels is CORRECT?

Question

BlackTom AI · Accepted Answer

Ligand-gated ion channels open when a neurotransmitter (ligand) binds to them, creating a pore that permits ions to flow across the cell membrane and thereby change the postsynaptic cell’s membrane potential.

Relevant knowledge points and concepts:
- Ligand-gated (ionotropic) receptors are membrane proteins that undergo a conformational change on transmitter binding and form an ion-conducting pore. Examples: nicotinic acetylcholine receptors, GABA(A) receptors, glycine receptors, and 5-HT3 receptors.
- They mediate fast synaptic transmission at the postsynaptic membrane (e.g., at neuromuscular junctions and many central synapses).
- Ion selectivity varies by receptor type: some are cation channels (Na+, K+, sometimes Ca2+), others are anion channels (Cl–).
- These are distinct from voltage-gated ion channels (which open in response to membrane depolarization and are concentrated at the axon initial segment) and from G-protein–coupled (metabotropic) receptors (which act via intracellular second messengers).

Step-by-step reasoning:
1. The defining functional feature is opening in response to ligand binding and allowing ions to pass — this matches statement 1.
2. Statement 2 claims they are highly selective and only allow sodium into the neuron. This is false: many ligand-gated channels are nonselective cation channels (permit Na+ and K+, e.g., nicotinic ACh) or are anion-selective (GABA(A) passes Cl–), so “only sodium” is incorrect.
3. Statement 3 misattributes the axon initial segment localization and action potential initiation to ligand-gated channels; in fact voltage-gated Na+ channels at the initial segment initiate action potentials.
4. Statement 4 incorrectly classifies ligand-gated ion channels as G-protein–coupled receptors; GPCRs are metabotropic and signal via second messengers rather than forming pores.

Why the correct answer is correct:
Statement 1 precisely describes the mechanism of ligand-gated ion channels: transmitter binding opens the channel to allow ion movement across the membrane, producing fast synaptic effects.

Conclusion: The correct answer is "Ligand-gated ion channels are opened by binding of a transmitter to allow movement of ions across the cell membrane." This matches the provided answer.

Which one of the following statements about ligand-gated ion channels is CORRECT?Single choice

Similar Questions

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Ligand gated ion channels can be found:

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