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Cell nucleus. Coloured Transmission Electron Micrograph (TEM) of a slice through a liver cell, showing a large round nucleus and cell organelles. The nucleus is bounded by a double membrane con- taining pores that allow large molecules to pass out. The dark material inside the nucleus is chro- matin, a condensed form of DNA. Within this is a lighter area, the nucleolus, which contains unrav- elled DNA involved in making ribosomes (protein- manufacturing bodies). Outside the nucleus are mitochondria (round bodies, right), which provide the cell with chemical energy, and the endoplasmic reticulum (folded structure, top left), where proteins are made. Magnification unknown.
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