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.