[Campbell Biology P.1119] The text states that ion channels exhibit 'selective permeability.'... | Practice Question

The text states that ion channels exhibit 'selective permeability.' Given that potassium and sodium channels have similar overall structures, how do these proteins most likely differ to allow passage of only a particular ion?

  • A: By having different overall sizes that only fit specific ions.
  • B: By possessing different charges within their pore, repelling ions of the wrong charge.
  • C: By having different arrangements of amino acid side chains lining the pore, creating specific binding sites or steric hindrance for different ions.
  • D: By being activated by different types of neurotransmitters.

Explanation

Ion channel selectivity, even for ions of similar charge and size, is primarily determined by the precise atomic arrangement of the amino acid residues that line the channel pore. These residues interact differently with specific ions, allowing some to pass while excluding others, often involving dehydration and rehydration steps specific to ion size and charge, and the fit within the 'selectivity filter'.