[Structure of animal ribosomes. VI. Adynamic model of ribosome structure]

A dynamic model for the structure of ribosomes is developed using X-ray small-angle scattering data and electron micrographs of ribosomes and polysomes. The large subunit has the shape of a conical frustum, and has a groove at its flat side. The small subunit consists of two semiparticles which are connected by a molecular strand; it may assume two conformations: a prolate P conformation and an oblate O conformation. Translocation of the ribosome along the mRNA in the elongation process of protein synthesis is accomplished by cyclic conformation transitions P-O-P-O in combination with the linking and rupturing of bonds. This mechanism is called "rack and roll" mechanism.