What factors contribute to the selectivity of protein ion channels?

The selectivity of protein ion channels is primarily influenced by their shape, size, and electrical charge. Each ion channel has a specific structure that allows only certain ions to pass through, based on the physical dimensions and the properties of the ions.

The shape of an ion channel dictates which ions can physically fit through. For example, a channel may be large enough to allow potassium ions to enter while being too small for larger ions like calcium, thus maintaining selectivity based on size.

The electrical charge is also crucial for selectivity. Many channels contain regions that are charged, meaning that an ion with a matching charge might be attracted into the channel, while ions with opposing charges may be repelled. This characteristic makes it possible for channels to preferentially allow certain ions to pass through based on their charge.

Thus, these factors—shape, size, and electrical charge—work together to determine which specific ions are allowed through the channel, leading to the selective permeability that is essential for various physiological processes, such as nerve impulse transmission and muscle contraction.