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Potassium ( K + ) Channels

Decent Essays
Potassium (K+) channels are ubiquitous throughout biological systems as they are found in many different cell types including prokaryotes, eukaryotes and archaea. (However, for the scope of this exam, the examples will be limited to K+ channels found in neurons.) They are tetrameric integral membrane proteins that assemble to form transmembrane aqueous pores. Their basic function is to allow the passive flow of potassium ions down an electrochemical gradient rapidly and with high specificity. The high specificity of these channels is crucial in excitable cells such as neurons as they are able to exclude sodium ions (Na+) despite the sub-angstrom difference between ionic radii, which allows for the establishment of ion gradients as well as a delayed flow between sodium and potassium ions to shape action potentials. This specificity also allows the channels to establish and maintain the resting potential in many cells.
All potassium channels have a distinctive, universal feature of two transmembrane (TM) helices and a short loop (“P loop”) between them that lines the top of the pore and is responsible for potassium selectivity. This canonical feature is referred to as 2TM/P. In terms of membrane topology, there are two broad classes of K+ channels: 1) the two-transmembrane-helix (2TM/P) subunit, typical of the inward rectifying (KIR) channels and, 2) the 6-transmembrane-helix (6TM/P) subunit, typical of voltage-gated (KV ) subtypes. It must be noted that the 6TM/P
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