Final answer:
The ion selectivity of the voltage-gated potassium channel is based on its protein structure that responds to voltage changes, with specific amino acids creating a pore selective for K+ ions, allowing repolarization of the cell's membrane potential.
Step-by-step explanation:
The structural basis for the ion selectivity of the voltage-gated potassium (K+) channel relies on its specific protein structure that allows it to be sensitive to changes in transmembrane voltage. These voltage-gated channels have gates that open in response to a particular membrane voltage, typically at -50 mV. The ion selectivity is primarily determined by the size and shape of the ion channel, which matches the dimensions of K+ ions, as well as by the specific distribution of amino acids within the channel that interact with the K+ ions.
When the membrane potential approaches +30 mV, voltage-gated K+ channels open, permitting K+ ions to exit the cell and thus initiating repolarization. This return toward the resting membrane potential, typically around -70 mV, is crucial for the functioning of nerve and muscle cells. The patch-clamp technique, which has been used to study ion channels, shows how specific ions flow through these channels to generate cellular electrical activity such as action potentials.