Problem:

Question: Sodium and potassium ion channels have several negatively charged residues at the entry to the channel. On what basis do K channels specifically select for K ions? (In other words, why don\'t K channels enable Na ions to cross the membrane?) can have more than 1 answer...

1) ionic radius, Na is too small

2)energy cost, it is too energetically costly to dehydrate Na

3)charge, Na is slightly less electronegative than K and does not interact with the channel carbonyl groups

4)ionic radius, Na is too big

5)charge, Na is slightly more electronegative than K and does not interact with the channel carbonyl groups

Please choose correct option.