Eukayotic Cell (430x maginification)

A “mini-organ” which protects the genome from attack and potentially gives a glimpse into the evolutionary past of the Nucleus.

Eukaryotic cells, or any cells with a nucleus, contain almost all of the cells DNA in the nucleus, however some of the cell’s DNA exists in the cytoplasm, the fluid-filled body.  Foreign DNA from viruses and bacteria can also enter the cell.  These floating bits of genetic material are trapped by the newly discovered mini organ in cells named the “exclusome”.

Scientists have found that exclusomes lack nuclear pore complexes (mediates transport of macromolecules from nucleus to cytoplasm), but feature a double membrane and proteins, just like the nucleus. Ruth Kroschewski from the Institute of Biochemistry at ETH Zurich notes that “the exclusome envelope features gaps that can be seen in the nuclear envelope only in the early stages of its formation.” Inside the exlcusome the genetic material that codes for telomeres is found. Telomeres are the ends of chromosomes that protects them from being destroyed or damaged.  This shows that the exclusome envelope is much simpler.  DNA being held outside of the Nucleus is a rare discovery as very few organelles carry DNA.  “Perhaps the exclusome is a first attempt at producing a cell nucleus,” Kroschewski says.  Through cell division, they stay in existing cells but do not enter new ones. This mechanism might be “an evolutionary relic of cellular machinery.”

In AP Biology this year we have learned about the compartmentalization of cells and how organelles function in the cell.  The mitochondria and chloroplasts remind me of the exclusome because the mitochondria and chloroplasts have their own DNA, although I doubt they follow the endosymbiont theory as the DNA the exclusomes store is used in the chromosomes.  The exclusomes are also similar to lysosomes we studied, as they clean up the old cell parts like how the exlclusomes clean up floating bits of potentially harmful genetic material.  The exclusomes are an interesting discovery to learn about the history in the creation on the nucleus and eukaryotic cells as a whole.  Also to learn that there are still mini organs or potentially organelles still being discovered makes me want to participate in the discoveries in the future. Do you think the exclusome is an organelle, or a mini-organ, or just a structure in the cell?  What else do you think can be learned about the history of cells from the exclusome?


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