Question
The acetylcholine receptor protein is a pen- tamer of five peptide subunits conceptually forming a five-sided ring, with the central portion serving as the transduction ion channel. Only two of the five subunits are involved in acetylcho- line binding. The remaining three peptide subunits participate in the signal transduction process that involves a protein conforma- tional shift, allowing inward movement of sodium ions through the [closed/opened] ion channel.