Figure 4-34. Overall structure of the E. coli ribosome at 25-Å resolution inferred from cryoelectron microscopy and three-dimensional reconstruction based on the analysis of 4300 individual projections.
Figure 4-34. Overall structure of the E. coli ribosome at 25-Å resolution inferred from cryoelectron microscopy and three-dimensional reconstruction based on the analysis of 4300 individual projections.

Figure 4-34Overall structure of the E. coli ribosome at 25-Å resolution inferred from cryoelectron microscopy and three-dimensional reconstruction based on the analysis of 4300 individual projections

(a) This model shows the shapes of the large (blue) and small (yellow) subunits of the ribosome with three aminoacyl-tRNAs (pink, green, yellow) superimposed at the A, P, and E sites. The roles of these tRNA-binding sites during protein synthesis are discussed later. Chemical cross-linking experiments have demonstrated that the mRNA (orange beads) passes close to the anticodon loops of the tRNAs and that the nascent polypeptide chain is buried in the tunnel in the large ribosomal subunit that begins within 10 – 15 Å of the 3′ aminoacylated end of the tRNAs. The tunnel termination site on the ribosome surface has also been accurately mapped. (b) Large panel shows a field of 70S ribosomes. Small panels (left) show cryoelectron microscopy images of a single 70S ribosome, small (30S) subunit, and large (50S) subunit. Small panels (right) show computer-derived averages of many dozens of images in the same orientation. Cryoelectron microscopy is carried out on unstained samples of ribosomes or subunits flash frozen as “vitreous ices” (without ice crystals) in a very thin layer of water (Chapter 5). Individual images are analyzed by computer projections. [See R. K. Agrawal et al., Cell, in press; J. Frank, 1995, Nature 356:441; J. Frank et al., 1995, Biochem. Cell Biol. 73:757. Courtesy of J. Frank.]

From: Section 4.4, The Three Roles of RNA in Protein Synthesis

Cover of Molecular Cell Biology
Molecular Cell Biology. 4th edition.
Lodish H, Berk A, Zipursky SL, et al.
New York: W. H. Freeman; 2000.
Copyright © 2000, W. H. Freeman and Company.

NCBI Bookshelf. A service of the National Library of Medicine, National Institutes of Health.