Question

To pass through the pore of an ion channel, what must be true of an ion? (Photo)

Choose one:
It must interact with polar groups in the narrowest part of the channel.
It must be positively charged.
It must interact with non-polar groups in the selectivity filter.
It must surround itself with water molecules.It must avoid contact with the channel wall.

Answer 1

For an ion to pass through an ion channel, it must be charge-selective; channels have domains to interact with specific ion charges and exclude certain sizes, allowing selective ion permeability.

Step-by-step explanation:

To pass through the pore of an ion channel, an ion must be selective for charge. Ion channels are specialized proteins that allow ions to cross the cell membrane in response to concentration gradients. These channels are characterized by the specific properties of amino acids in their structure, such as hydrophobic and hydrophilic domains, which interplay with the ion's charge.

Channels for positive ions (cations) have negatively charged side chains, while channels for negative ions (anions) have positively charged side chains, a phenomenon known as electrochemical exclusion. Additionally, ion channels are designed with specific pore sizes that can cause size exclusion, where water molecules surrounding the ions may impede or allow the ions' passage through the channel, depending on their size. Larger pores are not ideal for smaller ions due to more significant interaction with water molecules than with amino acid side chains. This specificity ensures that certain ions, like Na+, K+, and Ca²+, can move selectively through these channels while excluding others.