Mitochondria are energy-producing compartments found in nearly all eukaryotic cells (cells that contain a nucleus that houses the DNA). The energy that mitochondria produce is in the form of ATP, an energy rich molecule that powers much of the work cells do. The process of producing ATP from glucose and oxygen is called oxidative phosphorylation.
Mitochondria are descended from bacteria (specifically, the alpha-proteobacteria) that formed an endosymbiontic relationship with the ancestors of our cells probably around two billion years ago (see figure). On the otherhand, the origins of eukaryotic cells are uncertain although they appear to be a the product of the fusion between some kind of bacteria and another bacterial-like cell called an archeabacterium.
Cells cannot make mitochondria from scratch and can only make new ones by dividing mitochondria already present in the cell. When mitochondria divide they simply pinch into two, though not necessarily into equal halves. Bacteria divide also this way which makes sense since they are the ancestors of mictochondria. It follows then that mitchondria may still use the same set of proteins to divide as bacteria. Many proteins are involved in bacterial division and the most widely occuring and conserved division protein is FtsZ. Just prior to division FtsZ molecules assemble to form a ring around the inside of the cell called the Z-ring. This ring appears to constrict pulling the edges of the cell until it splits into two.
In the cells of the most well studied eukaryotic organisms, such as animals and yeast, FtsZ is not present and their mitochondria appear to employ dynamin-like proteins to carry out mitochondrial division. Recently however, mitochondrial forms of FtsZ were discovered in other organisms such as algae and slime molds. Evidence for the involvement of FtsZ in mitochondrial division first came from the alga, Mallomonas splendens. Recently, we have discovered that the amoeba, Dictyostelium discoideum, also uses FtsZ to divide its mitochondria.
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