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by Wayne Decatur
The 2009 Nobel Prize in Chemistry was awarded for studies of the ribosome. The ribosome is the machine in your cells that accurately and efficiently decodes the genetic information stored in your genome and synthesizes the corresponding polypeptide chain one amino acid at a time in the process of translation. These structures are considered landmarks for the fact they showed clearly the major contributions to decoding and peptide bond synthesis come from RNA and not protein, as well as for the sheer size of the structures determined.

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Y Gu, V Srikanth, AI Salazar-Morales, R Jain, JP O'Brien, SM Yi, RK Soni, FA Samatey, SE Yalcin, NS Malvankar. Nature 2021 doi: 10.1038/s41586-021-03857-w
Geobacter pili were long thought to be electrically conductive protein nanowires composed of PilA-N. Nanowires are crucial to the energy metabolism of bacteria flourishing in oxygen-deprived environments. To everyone's surprise, in 2019, the long-studied nanowires were found to be linear polymers of multi-heme cytochromes, not pili. The first cryo-EM structure of pili (2021) reveals a filament made of dimers of PilA-N and PilA-C, shown. Electrical conductivity of pili is much lower than that of cytochrome nanowires. Evidence suggests that PilA-NC filaments are periplasmic pseudopili crucial for exporting cytochrome nanowires onto the cell surface, rather than the pili serving as nanowires themselves.

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The Capsid of a virus is its outer shell or "skin". Viruses have evolved intricate and elegant ways to assemble capsid protein chains into complete, usually spherical capsids, often with icosahedral symmetry. Pictured is an extremely simplified model of a capsid, where a single enlarged atom represents each of the 360 protein chains in the capsid of the Simian Virus 40 (SV40), a member of a group of cancer-causing viruses that has been extensively researched for decades.

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