Nucleolus conditions

The number and size of mitochondria indicate the level of energy metabolism and vary according to the condition of the fish (Ozemyuk, 1985 Savina, 1992), as does the level of nucleolus-protein biosynthesis (Arkhipchuk and Makarova, 1992). 

Because the activity of the nucleolus is closely linked to the overall metabolic state of the cell, a number of model systems have been developed to study activation of the nucleolus from a minimal resting state. One of the best studied systems is the isolation of human peripheral blood mononuclear cells by means of a Ficoll gradient and the subsequent culture in media to which has been added the mitogenic plant lectin phytohemagglutinin (Busch and Smetana, 1970 Wachtler et ai, 1980 Ochs and Smetana, 1989). Under these culture conditions, T lymphocytes are induced to grow and eventually divide, starting from a resting... 

However, the nucleus also always contains some RNA located in the nucleolus (which does not contain DNA) and in the chromatin filaments. The ratio RNA/DNA varies from one spedes to another and, in the same spedes, from one organ to another. Unlike DNA whose composition is characteristic of all the cells of a spedes, the composition of RNA varies in the same cell from one point to another. Thus the RNA of the nucleus, the microsomes, and the mitochondria are all of different composition. Physiological conditions can also modify the composition of the various types of RNA in an organism, although they have no influence on the composition of the DNA. 

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