Principles of Biochemistry Volume 3 - A. Lehninger 1985

Molecular mechanisms of genetic information transfer
Protein synthesis and its regulation
Eukaryotic cytoplasmic ribosomes are larger in size and have a more complex structure

Extramitochondrial Ribosomes of Eukaryotic Cells are significantly larger than prokaryotic ribosomes (Fig. 29-11). They have a diameter of approximately 21 nm, a sedimentation coefficient of 80S, and a molecular weight reaching 4 ∙ 106 daltons. Like prokaryotic ribosomes, they consist of two subunits whose size varies among species, averaging 60S and 40S. The small subunit contains 18S rRNA, while the large subunit includes 5S, 5.8S, and 28S rRNAs. In total, eukaryotic ribosomes contain over 70 different Proteins. The rRNA and the majority of proteins of eukaryotic ribosomes have also been isolated and characterized.

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Fig. 29-13. The ribosomal subunits of E. coli exhibit a complex shape revealed by X-ray crystallography and Electron Cell/15.html">Microscopy. A. Models of the 30S (top) and 50S (bottom) subunits shown from different angles. B. The assembled 70S ribosome shown in two different orientations. The 30S subunit is light-colored, and the 50S subunit is dark-colored.

The two ribosomal subunits are not joined together continuously. As we will see below, each time the synthesis of a new polypeptide chain begins, the ribosomes must dissociate into their constituent subunits.



Last update: 06/08/2026

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