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6.11.1. Characteristics of the cell nucleus

Characteristics of the cell nucleus

It is found in all eukaryotic cells, where it is their vital center and the one that contains genetic information (in addition to that contained in mitochondria and chloroplasts).

Normally there is only one nucleus per cell, but exceptionally there may be more. As for example, in cases where they occur:

  • Syncytios: due to the disappearance of the membrane of several uninucleated cells, leaving a single multinucleated cell. Example: in muscle cells.
  • Plasmodia: there are several nuclear divisions without division of the cytoplasm. For example, the protozoan Opalina ranarum, a parasite of the digestive tract of frogs, with several dozen nuclei.

The nucleus of plant cells, during the interphase, is usually discoidal and is usually in a lateral position , due to the pressure exerted by the vacuoles.

In animal cells, the interphase nucleus is usually spherical and is in a central position .

The shape of the nucleus depends on cell activity and the shape of the cell. The nucleus is more irregular the more activity it has. Isodiametric cells usually have spherical nuclei; prismatic and spindle cells, ovoid nuclei; flattened cells (endothelium), discoidal nuclei; in neutrophils , lobed nuclei, ...

The size of the nucleus varies greatly, although it is usually larger in the more active cells. For each type of cell there is a nucleoplasmic relationship (RNP) between the volume of the nucleus and the volume of the cytoplasm, which remains constant. If the value is lower because the cytoplasm has grown a lot, the nucleus cannot control as much volume, and it is time to begin cell division.