Nucleus is the heaviest particulate component of the cell. Except matured mammalian erythrocytes, nucleus is found in almost all cells. The nucleus about 4-6µm in diameter is surrounded by a perinuclear envelope. At various position the outer membrane of the envelope fuses with the inner membrane to form pores (Fig. 1.4). Nuclear pores provide continuity between the cytosol and the contents of the nucleus (nucleoplasm). The electron microscope reveals that the nuclear content consist of granular or fibrillar structures. The nucleolus, a discrete body within the nucleus, contains ribonucleic acids (RNA). The most important component of the nucleus is an organised clumps of threadwork known as chromatin which is distributed throughout the nucleus and contains most of the cellular deoxy ribonucleic acids (DNA). Immediately before the cell division the chromatin organises into simple thread like structures known as chromosomes which will eventually be distributed equally to each daughter cell.
Take part in cell division Contain DNA molecules which are heriditary carriers.