Question

A membrane spanning protein that is a channel for potassium ion transport is made up of six copies of a single polypeptide. Potassium ions are transported across the membrane using the channel. The potassium channel has:

a. Tertiary structure

b. Quaternary structure

c. Secondary structure

d. Primary structure

Answer 1

b. Quaternary structure

Potassium channels have a tetrameric structure ( A tetrameric protein is a protein with a quaternary structure of four subunits) in which four identical protein subunits associate to form a fourfold symmetric (C4) complex arranged around a central ion conducting pore (i.e., a homotetramer). Alternatively four related but not identical protein subunits may associate to form heterotetrameric complexes with pseudo C4 symmetry. All potassium channel subunits have a distinctive pore-loop structure that lines the top of the pore and is responsible for potassium selective permeability.