Full Question Options!
-ionic radius, Na+ is to small
-energy cost, it is to energetically costly to dehydrate Na+
-charge, Na is slightly more electronegative than K and does not interact with the channel carbonyl groups
-charge, Na is slightly less electronegative than K and does not interact with the channel carbonyl groups
-ionic radius, Na+ is too big
Answer:
-ionic radius, Na+ is to small
Explanation:
Potassium channels are designed to allow the flow of potassium ions across the membrane, but to block the flow of other ions--in particular, sodium ions. These channels are typically composed of two parts: the filter, which selects and allows potassium but not sodium to pass, and the gate, which opens and closes the channel based on environmental signals.
The selectivity filter in the potassium channel have oxygen atoms that are too far apart to stabilize a dehydrated sodium ion. The selectivity filter in the sodium channel is too small for a partially hydrated potassium ion.
Sodium ions, are slightly smaller in size, so they fail to interact with the oxygen atoms lining the pore wall.
