A dense, spherical structure within the nucleus where ribosomal RNA is synthesized and ribosome assembly begins. It's the most prominent feature visible in the nucleus under a microscope.
From Latin 'nucleolus', the diminutive of 'nucleus', literally meaning 'little nucleus'. First described in the 1830s as a small, dense spot within the cell nucleus, though its function wasn't understood until the 20th century.
The nucleolus is like a ribosome factory that works so hard it glows! It's not surrounded by a membrane but forms spontaneously around the genes that make ribosomal RNA - when cells need more protein-making machinery, the nucleolus literally gets bigger and more active.
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