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 dont k+ channels enable na+ ions to cross the membrane? )
a. ionic radius, na+ is to smallb. energy cost, it is to energetically costly to dehydrate na+c. charge, na is slightly more electronegative than k and does not interact with the channel carbonyl groupsd. charge, na is slightly less electronegative than k and does not interact with the channel carbonyl groupse. ionic radius, na+ is too big

A. Ionic radius, Na⁺ is to small.

Explanation:

The channel pore contains a narrow selective filter that is delimited by carbonyl oxygens (C = O) of the polypeptide skeleton. When a K⁺ ion enters the selection filter it interacts with these carbonyl oxygens, and the water molecules to which the K⁺ was attached move, allowing the dehydrated K⁺ to pass through the pore. However, a dehydrated Na⁺ is too small to interact with these carbonyl oxygens in the selective filter, which is kept open. As a consequence, this hydrated sodium ion is too large to pass through the canal.

where in your body is there an enzyme that does function at a high or low ph? what is the name of that enzyme and its function?