In eukaryotic cells around 99% of total cellular DNA is localized within the nucleus. The remaining is contained in the mitochondria and chloroplasts, coding some proteins which play essential roles for the functioning of these organelles. However, members of the Protist Kingdom contain extranuclear DNA molecules either within the mitochondria, but presenting a distinct structural organization, as occurs with the kinetoplast of trypanosomatids or located in another cytoplasmic structure such as the apicoplast described in the organisms of the Apicomplexa Phylum. Moreover, several organelles related to the mitochondria have been described in a number of parasitic protozoa, although these compartments lack a detectable organellar genome. As examples we can mention the mitosomes, found in protozoa such as Giardia lamblia and Entamoeba histolytica and the hydrogenosomes found in organisms such as Tritrichomonas vaginalis. Here we will briefly review the most important information concerning these structures.
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