Astonishing Complexity In Cell Systems

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Gene expression in eukaryotic cells

I conservatively counted 24 recently discovered mechanisms that help regulate gene expression in eukaryotic cells, as reviewed by Moore and Proudfoot.1 Here are just a few of them.

Figure 1.

Figure 1. Widely regarded as the simplest genome, Mycoplasma gene expression is instead far more complicated than expected. It performs functions that had been considered the sole domain of higher eukaryotes. For example, DNA is transcribed in both the sense and antisense directions, indicating that valuable genetic information is double-stacked. RNA transcripts undergo post-translational modifications, single enzymes have more than one application, and when certain metabolic breakdowns occur, the cell is able to formulate a workaround solution. Illustration after. sciencemag.org

Chromatin is not loosely wadded DNA inside cellular nuclei. Instead, it is very precisely organized, with specific portions dynamically looped outward. Each loop is associated with a separate nuclear pore, and can retract to a storage position when appropriate. Robust and efficient machinery ensures that the correct portions of chromatin are unspooled from nearer the center of the nucleus to an appropriate nuclear pore. Each pore is extremely active, with a host of interacting regulatory RNA’s, proteins, and ribonucleoproteins.2 These send and receive communications from and toward the farthest ends of the RNA and protein manufacturing processes.

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