Leak channels are non-gated, perpetually open transmembrane proteins essential for setting a cell’s resting membrane potential by allowing passive ion flow down electrochemical gradients. Primarily comprising potassium and sodium types, these channels are crucial for neuronal excitability, muscle function, and maintaining ion homeostasis. These channels are incredibly size selective. Which of the following ions would be most similar in size to potassium and why would it still be unlikely to pass through a potassium channel?
A. Li+ but are still likely too small to pass through
B. Ca2+ but are still likely too large to pass through
C. Mg2+ but are still likely too small to pass through
D. Ca2+ but are still likely too small to pass through
Click for Explanation
The correct answer is D. While calcium ions would not move through potassium channels, they are most similar in size to a potassium ion. This is because a calcium ion is isoelectronic to a potassium ion, meaning they have the same electron configuration. However, as an ion gains more positive charge, its atomic radius will decrease. So while calcium and potassium ions have the same electron configuration, calcium would be a smaller ion and would be unable to form the same types of interactions with the ion channel, making it not energetically favorable to pass through.
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