Intro | Cytoplasm | Endoplasmic Reticulum | Golgi Complex | Microtubules | Mitochondria | Nucleus | Plasma Membrane | Ribosomes

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Mitochondria are the "powerhouses" of the cell. Aerobic (oxygen-based) metabolism of nutrients within the membrane structure of mitochondria is used to synthesize adenosine triphosphate (ATP). The ATP molecule stores energy within its chemical bonds, releasing this energy to fuel cellular processes as needed. Mitochondria are oval shaped and composed of a double lipid membrane. The inner membrane folds to form shelf-like extensions called cristae, where the majority of energy is produced.


It is estimated that the first of living cells, prokaryotes, emerged approximately 3.5 billion years ago (Arms & Camp, 1995). A popularly held belief, the endosymbiotic hypothesis, holds that eukaryotic cell arose from prokaryotic cells. Approximately 2 billion years after the first appearance of life, a large amoeboid-like prokaryotic cell ingested a small aerobic (oxygen-utilizing) bacterium. Instead of being digested, the bacterium was established within as an endosymbiont. Over time the bacterium developed into a mitochondrion and was incorporated into the life process of the cell. The oxygen-based metabolism of the bacterium provided the newly formed eukaryotic cell with a metabolic advantage.

The endosymbiotic hypothesis was generated in part in an attempt to explain the finding that mitochondria contain their own genetic material, DNA and RNA molecules. When a cell's need for energy production increases, a mitochondria can simply pinch into two. The two halves increase in size, thereby increasing the ability to produce ATP.


Arms, K. & Camp, P. (1995), Biology (4th ed.). New York: Harcourt Brace College Publishers.