Every living organism is categorized as either a prokaryote (having single chromosomes) or eukaryote (having pairs of chromosomes). Eukaryotes also contain a nucleus surrounded by a membrane, and its DNA is bound together by proteins (histones) into chromosomes. Eukaryotic cells are also distinct by “containing endoplasmic reticulum and numerous specialized organelles not present in prokaryotes––especially mitochondria, Golgi bodies, and lysosomes.”
Who said that science can ever be “settled”? This report [below] goes against the long-standing dogma that eukaryotes by definition must contain mitochondria organelles.
Mitochondria (as the “energy-producers” of the cell) are “well known to be essential cellular components in all eukaryotes.” In the attached report, authors describe the genome sequence of a microbial eukaryote, the oxymonad Monocercomonoides sp., which reveals that this organism lacks all hallmark mitochondrial proteins. Perhaps even most importantly, the mitochondrial iron-sulfur (Fe–S) cluster assembly pathway, thought to be conserved in virtually all eukaryotic cells, has been replaced by a cytosolic sulfur mobilization system (SUF) acquired by lateral gene transfer from bacteria.
In the context of eukaryotic phylogeny, these exciting data suggest that Monocercomonoides is not primitively amitochondrial, but rather, as a function of evolutionary time, has lost the mitochondrion secondarily. This is the first example of a eukaryote lacking any form of a mitochondrion, demonstrating that this organelle is not absolutely essential for the viability of a eukaryotic cell !!
Curr Biol 2o16; 26: 1274–1284