Both voltage-gated and ligand-gated ion channels are large protein molecules, as is the sodium pump Na,K-ATPase. In recent years the primary structure of a number of them has been determined, and by combining this information with the biophysical evidence, major advances have been made in our understanding of how they work at the molecular and submolecular levels.

cDNA sequencing studies

A protein consists of a long chain built up of 20 different amino acids (Table 5.1), folded on itself in a rather complicated way. Its properties depend critically on the arrangement of the folds, which is determined by the exact order in which its constituent amino acids are strung together. This in turn is specified by the sequence of the nucleotide bases that make up the DNA molecules which constitute the genetic material of the cell. There are only four different bases, and each of the 20 amino acids corresponds according to a universally obeyed triplet code to a specific group of three of them. The information embodied in the base sequence of a DNA molecule is transcribed on to an intermediary messenger RNA, and is then translated during the synthesis of the protein to yield the correct sequence of amino acids. Rapid sequencing methods for nucleotides were perfected by Sanger and his colleagues, and modern recombinant DNA technology makes possible the cloning of DNA so that the quantity required for the determination can be prepared from a single gene.