DON FAWCETT / SCIENCE PHOTO LIBRARY DON FAWCETT / SCIENCE PHOTO LIBRARY
Cell nucleus. Coloured scanning electron micrograph (SEM) of a freeze fractured cell nucleus (red) and cytoplasm (green). The nucleus is bounded by a nuclear membrane containing gaps (nuclear pores, pink) that allow large molecules to pass out of the nucleus. The nucleus of a cell contains a complete set of the organism's genes, which are encoded into DNA molecules on chromosomes. Freeze fracturing involves rapidly freezing the cell before fracturing it with a sharp edge. It provides a facing view of membranes, rather than the cross-sectional view provided by normal techniques. Magnification unknown.
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