Question

What is a "selectivity filter"' of an ion channel? Do all channels contain a selectivity filter?

Short answer

Answer: The role of a selectivity filter in ion channels is to confer ion selectivity by allowing specific ions to pass through while restricting others. This is based on the size and charge of the ions. Not all ion channels have a selectivity filter; non-selective ion channels can allow a wider range of ions to pass through them.

Step-by-step solution

Define Ion Channels

Ion channels are proteins embedded within cell membranes that create a pathway for the transport of ions across the membrane. They facilitate the passage of specific ions like sodium, potassium, calcium, and chloride, which help in maintaining the electrochemical gradients and control various cellular processes.

Explain the role of selectivity filters

A selectivity filter is a crucial part of an ion channel that confers its ion selectivity. It is a narrow, specialized region within the channel's pore that allows the specific ions to pass through, while restricting other ions or molecules. The selectivity filter primarily relies on the size and charge of the ions and has a complementary structure that can interact with the target ion.

Discuss ion selectivity in channels

Not all ion channels are selective for a specific type of ion. Some channels are classified as non-selective or "leaky" channels, which allow ions to pass regardless of their charge or size. This lack of strict selectivity is possible because their selectivity filters are less discriminatory in terms of size and charge, or are not present in the channel structure.

Conclusion

A selectivity filter is a crucial part of an ion channel that determines its ion selectivity. It enables specific ions to pass through the ion channel while restricting others. Not all ion channels have a selectivity filter, and non-selective ion channels allow a wider range of ions to pass through them.