Ribosome Structure And Function

19.1. Introduction

In this concluding chapter an attempt to formulate several general principles of the structure and function of the ribosome is undertaken. The reservation should be made that our understanding of the ribosome is far from complete, and the formulations reflect only the today's level of the knowledge. Concerning the ribosome structure, the principles formulated can be considered as a summary of factual information and its generalization, whereas the principles of the function are rather hypothetical and represent just plausible models. Nevertheless, this seems to be the first attempt to give a generalized conceptual vision of the ribosome and to co-ordinate the structure and the function. From both scientific and educational point of view, such tentative formulations may be a useful appendix to the main course of experimental ribosomology.

19.2. Basic Features of Ribosome Structure

19.2.1. Two Disparate Subparticles (Ribosomal Subunits)

The ribosome is a compact particle that can be roughly approximated by a sphere with a diameter of about 30 to 35 nm. Its structure lacks any internal or external symmetry. The most prominent physical feature of the particle is its subdivision into two unequal asymmetric subparticles, or ribosomal subunits.

The subdivision can be easily demonstrated by electron microscopy: a deep groove along the ribosome separates the large and the small subunits (Fig. 5.2). Upon decrease of Mg2+ concentration in the medium, the ribosome dissociates into the two subunits. The dissociation can be recorded by ultracentrifugation (Fig. 5.3). During dissociation the homogeneous ribosomal particles with sedimentation coefficient of 70S in the case of prokaryotic ribosomes or 80S in the case of eukaryotic ribosomes convert into two-component mixture of 50S and 30S, or 60S and 40S particles, respectively:

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