PROFESSORS P. MOTTA & T. NAGURO / SCIENCE PHOTO LIBRARY PROFESSORS P. MOTTA & T. NAGURO / SCIENCE PHOTO LIBRARY
Nucleolus and chromatin fibres. Coloured high resolution scanning electron micrograph (SEM) of the nucleolus and chromatin fibres of a primordial testis germ cell nucleus (8-week-old human embryo). The nucleolus (centre left) is a specialized region of the nucleus (pink). It is the site for synthesis of ribosomal RNA and proteins. Surrounding the nucleolus are chromatin fibres which contain the chromosomes. The chromosomes hold the genetic instructions for an organism but only become visible when the cell divides. Separating the nucleus from the cytoplasm (at right) is the nuclear membrane (thin line).
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