K.R. PORTER / SCIENCE PHOTO LIBRARY K.R. PORTER / SCIENCE PHOTO LIBRARY
Mitochondrion. Coloured Transmission Electron Micrograph (TEM) of a mitochondrion inside a human cell, showing the double outer membrane and numerous internal membranes (cristae) where respiration takes place. The folded structure outside the mitochondrion (upper left) is rough endoplasmic reticulum, where the cell's proteins are made. Mitochondria provide cells with energy by oxidising sugar and fat. They are found in almost all cells (sometimes times in thousands), carry their own DNA, and replicate autonomously. Mitochondria are thought to have evolved from a once free-living type of bacteria that formed a symbiotic partnership with primitive cells. Magnification unknown.
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