Voltage-Gated Channels

Large size: Necessary to create a pore for ions to pass through the membrane.
Six transmembrane regions: Form an opening in the membrane.
Central pore: Key feature with amino acids lining the pore.
Selectivity filter: The spacing and properties of the amino acids determine which ions can pass through.

Amino acid distance: Appropriately spaced for potassium ions with water molecules.
Potassium ion interaction: Amino acids interact with water molecules around the potassium ion to remove them.
Process: Allows potassium to pass through without water molecules.
Selectivity: Selects for potassium ions based on size and amino acid spacing.

Sodium ion size: Sodium is smaller than potassium.
Sodium interaction: Water around sodium only interacts with amino acids on one side of the pore.
Incomplete dehydration: Water molecules cannot be fully removed from sodium.
Prevention: This prevents sodium from passing through the potassium channel.

Role: Critical for action potentials in neurons, similar to potassium channels.
Opening speed: Opens rapidly in response to a stimulus.
Mechanism: Channel gating.
Voltage sensor: Located in the fourth transmembrane region.
Function detection: Discovered through mutation experiments, where changing specific amino acids eliminates channel function.
Pore structure: Similar to potassium channels, with amino acids lining the pore.
Sodium ion interaction: Amino acids spaced perfectly for sodium ions to pass through after water removal.
Selectivity filter: Distance between amino acids in the pore determines ion selectivity.

Potassium vs Sodium pore size: Primary distinction lies in the spacing/distance between amino acids in the pore which determines the size of the ion they allow to pass.