Which of the following best describes a ligand-gated ion channel?

• A. An ion channel that opens in response to the binding of a specific molecule, such as a neurotransmitter.
• B. An ion channel that opens in response to mechanical deformation of the cell membrane.
• C. An ion channel that is always open and allows ions to pass freely.
• D. An ion channel that opens in response to changes in membrane potential.

Answer: (A)

Verified step by step guidance

1. Step 1: Begin by understanding the term 'ligand-gated ion channel.' A ligand-gated ion channel is a type of membrane protein that opens or closes in response to the binding of a specific molecule, known as a ligand. This ligand is often a neurotransmitter or other signaling molecule.
2. Step 2: Compare the definition of a ligand-gated ion channel to the options provided. The correct description should match the mechanism where the channel opens due to the binding of a specific molecule.
3. Step 3: Eliminate options that describe other types of ion channels. For example, channels that open due to mechanical deformation are called mechanosensitive channels, and those that open due to changes in membrane potential are voltage-gated ion channels.
4. Step 4: Consider the option describing an ion channel that is always open. This does not match the definition of a ligand-gated ion channel, as ligand-gated channels require a specific molecule to bind for activation.
5. Step 5: Select the option that accurately describes a ligand-gated ion channel: 'An ion channel that opens in response to the binding of a specific molecule, such as a neurotransmitter.' This matches the definition and mechanism of ligand-gated ion channels.