According to the Biology Online dictionary, an organelle can literally be defined as a little organ. “As the body is composed of various organs, the cell, too, has "little organs" that perform special functions. They are membrane-bound compartments or structures of a cell” (n.d.). One of the most unique organelles is that of the mitochondria.
There is a theory of thought accepted by most biologists now that the mitochondria actually originated as symbiotic bacteria (Alters & Alters, 2006). Doctor Lynn Margulis proposed that the mitochondria, because they appear to only originate from other mitochondria, and because they contain their own DNA, were actually descendants of formerly free-living bacteria. This idea is known as the endosymbiont hypothesis or theory (depending on what you read). The suggestion is that the eukaryotic cells retained the bacteria because they could not carry out the necessary chemical reactions required to survive in an atmosphere where oxygen was on the increase (Alters & Alters, 2006). Doctor Margulis is accredited with this theory, but the idea was actually first suggested by a Russian botanist, Konstantin Mereschkowsky in 1905. As noted in the New World Encyclopedia, “Mereschkowsky was familiar with work by the German botanist Andreas Schimper, who had observed in 1883 that the division of chloroplasts in green plants closely resembled that of free-living cyanobacteria, and who had himself tentatively proposed (in a footnote) that green plants had arisen from a symbiotic union of two organisms” (n.d.).
The mitochondria have rod-shaped bodies and are very similar in size and shape to certain bacteria. They contain outer and inner membranes with the outer being smooth and defining shape and the inner being convoluted with folds called cristae. “The cristae resemble the folded membranes that occur in various groups of bacteria” (Alters & Alters, 2006). Again giving credence to the endosymbiont theory.
The mitochondria function as ‘cellular power plants', their primary job “is to break down fuel molecules releasing energy for cell work” (Alters & Alters, 2006). Basically they take in the nutrients and break them down thereby energizing the cell. This process is known as cellular respiration. This is an extremely important function as the “energy released is stored for later use in special molecules called ATP” (Alters & Alters, 2006). Adenosine triphosphate (ATP) is the chief supplier of immediate energy needs. Food taken in by cells is stored so that the cells can supply energy ‘at a moment's notice'. Without this imperative function of the mitochondria, all living things would find they're energy supply sapped shortly after consuming food. Mitochondria are also unique because the number of them can differ from cell to cell, some cells only require a single mitochondrion, yet others such as a muscle cell, may require many thousands, because of the energy needed by that muscle cell.
The mitochondria play an incredibly important part within the organelle family. Their uniqueness and origins differentiate them from the other organelles yet their primary function as powerhouses means they play an integral role within the cell.
Alters S. and Alters B. (2006). Biology understanding life. Hoboken, NJ. John Wiley & Sons, Inc..
Margulis, Lynn. (n.d.) In New World Encyclopedia. Retrieved from http://www. newworldencyclopedia.org/entry/Lynn_Margulis
Organelles. (n.d.) In Biology-online dictionary. Retrieved from http://www.biology-online.org/dictionary/Organelles.
Sullivan, Jim. (n.d.) Cells Alive. Mitochondria. Retrieved from http://www. cellsalive.com/cells/mitochon.htm.