Ion channels

Question 1

Ion channel

Answer 1

A transmembrane protein that allows the selective flow of ions across cell membranes, enabling cells to establish and alter their resting membrane potential and communicate electrically.

Question 2

Structural requirements for ion channels

Answer 2

Consist of pore-forming subunits, have hydrophilic and hydrophobic domains, have transmembrane segments, selectivity filters, voltage sensors and gating mechanisms.

Question 3

Protein structure diagrams

Answer 3

Voltage-dependent potassium channels: Tetrameric structure with six transmembrane segments (S1-S6) and a P-loop that lines the selectivity filter.

Voltage-dependent sodium channels: Tetrameric structure with four homologous domains, each with six transmembrane segments (S1-S6).

Nicotinic AChRs: Pentameric structure with four transmembrane domains per subunit and a large extracellular domain for binding acetylcholine.

Question 4

Role of ion channels

Answer 4

Determine the membrane potential by selectively allowing ions to cross the cell membrane. Opening or closing channels changes the membrane potential, leading to changes in cell excitability. Membrane depolarization is an excitatory event because it makes the membrane potential less negative and closer to the threshold for action potential initiation.

Question 5

Families of ion channels

Answer 5

Classification by physiology: Voltage-gated channels, ligand-gated channels, and mechanically-gated channels.

Classification by pharmacology: Ionotropic and metabotropic receptors.

Classification by structure: Cation-selective, anion-selective, and non-selective channels.

Question 6

Properties of ion channels

Answer 6

Voltage-gated ion channel: Open or close in response to changes in membrane potential.

Ligand-gated ion channels: Open or close in response to binding of specific ligands (e.g. neurotransmitters).