Ligand Gated Ion Channels | Nervous system physiology | NCLEX-RN | Khan Academy

Summary

Ligand-gated ion channels are essential membrane receptors in cells, particularly neurons, that open or close in response to the binding of chemical messengers (ligands). These channels allow ions like sodium, potassium, and calcium to flow through the membrane, altering the cell's electrical properties and triggering an intracellular electrical signal. Ligand binding happens at an allosteric site, not directly on the channel itself. These channels differ from voltage-gated and stretch-activated ion channels, which rely on membrane potential and membrane deformation, respectively.

Takeaways

• 😀 Ligand-gated ion channels are integral membrane proteins that open or close in response to the binding of a chemical messenger (ligand).
• 😀 These channels are crucial for rapidly responding to stimuli in electrically excitable cells like neurons.
• 😀 Ligand-gated ion channels have an allosteric binding site where the ligand binds, separate from the channel itself, triggering a conformational change.
• 😀 The ligand binding causes the channel to open, allowing ions (like sodium, potassium, calcium, and chlorine) to move through the membrane.
• 😀 This movement of ions results in an intracellular electrical signal, converting the extracellular ligand signal into a cellular response.
• 😀 Only specific ligands can bind to specific channels, following the 'lock and key' or 'induced fit' model.
• 😀 These ion channels are scattered throughout the membrane and open/close simultaneously, leading to a rapid cellular response.
• 😀 Ligand-gated ion channels differ from voltage-gated ion channels, which respond to changes in membrane potential, not ligand binding.
• 😀 They are also distinct from stretch-activated ion channels, which are activated by the deformation or stretching of the cell membrane.
• 😀 The allosteric binding site is usually found on the extracellular side of the membrane, as these channels generally respond to external signals.
• 😀 Multiple allosteric binding sites may exist on a single ion channel, allowing different ligands to bind at various sites on the same protein.

Q & A

What are ligand-gated ion channels?

Ligand-gated ion channels are transmembrane proteins that open or close in response to the binding of a chemical messenger, called a ligand. These channels allow ions to pass through the membrane, causing changes in the cell's electrical properties.

Why are ligand-gated ion channels important in neurons?

Ligand-gated ion channels are essential in neurons because they enable quick responses to stimuli. Neurons need to react rapidly to chemical signals, and these channels facilitate this by allowing ions to flow into or out of the cell, altering its electrical state.

What happens when a ligand binds to a ligand-gated ion channel?

When a ligand binds to a ligand-gated ion channel, it causes a conformational change in the channel, which opens it. This allows specific ions, such as sodium, potassium, calcium, or chloride, to move through the membrane, creating an electrical signal inside the cell.

What is an allosteric site?

An allosteric site is a region on a protein that is distinct from the active site, where a ligand can bind. The binding of a ligand to this site causes a conformational change in the protein, affecting its activity, such as opening a ligand-gated ion channel.

How do ligand-gated ion channels differ from voltage-gated ion channels?

Ligand-gated ion channels respond to the binding of a ligand, while voltage-gated ion channels respond to changes in membrane potential. Voltage-gated channels open or close based on the electrical charge across the membrane, whereas ligand-gated channels are triggered by chemical signals.

What are the most common ions that pass through ligand-gated ion channels?

The most common ions that pass through ligand-gated ion channels are potassium, sodium, calcium, and chloride.

What is the role of ligand-gated ion channels in converting extracellular signals into intracellular signals?

Ligand-gated ion channels play a key role in converting extracellular chemical signals (ligands) into intracellular electrical signals. When the ligand binds to the channel, it opens, allowing ions to move across the membrane, creating an electrical signal inside the cell.

Can ligand-gated ion channels have multiple allosteric binding sites?

Yes, ligand-gated ion channels can have multiple allosteric binding sites. These sites are specific regions where different ligands can bind, potentially influencing the channel's opening or closing.

Why is the allosteric binding site usually located outside the ion channel?

The allosteric binding site is typically located outside the ion channel because membrane receptors like ligand-gated ion channels are designed to respond to extracellular signals. This allows the cell to detect and respond to chemical signals from the outside environment.

How do ligand-gated ion channels differ from stretch-activated ion channels?

Ligand-gated ion channels are activated by the binding of a ligand, whereas stretch-activated ion channels are triggered by the deformation or stretching of the cell membrane. The latter responds to mechanical stress rather than chemical signals.