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Prof. Eric Arnoys

bacterial 70S ribosome

This Protein of the Week selection coincides with our 2010 Merck/AAAS Lecture from Dr. Jamie Cate from Cal-Berkeley. The structures shown here of these wonderful molecular machines were decades in the making and represent a tremendous leap in our understanding of translation.

Ribosomes serve as the translators of the information contained in nucleic acids to the synthesis of proteins. Codons of three bases each correspond to one of twenty amino acids, which are added one at a time to the growing peptide chain within the ribosome.

70S ribosome

The bacterial 70S ribosome consists of two subunits, the smaller 30S subunit (in green, PDB code 2WDK, structure generated with PyMOL) and the larger 50S subunit (in cyan, PDB code 2WDL). The structure shows us that each subunit is actually comprised of many peptides as well as a large amount of rRNA.


When the colors are changed to reflect secondary structure (α-helices in red, β-sheets in yellow, and nucleic acids in green), the large amount of rRNA relative to the protein leaps out. In fact, ribosomes are ribozymes, in that RNA, rather than protein, provide the catalytic activity.

More information for exploring ribosomes can be found in its Molecule of the Month pages at RCSB Protein Data Bank.

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