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The nucleus is an intracellular compartment of the eukaryotic cell that contains the DNA.

The nucleus is composed of nuclear envelope and nucleoplasm.

Nuclear envelope contains the gates that allow communication between the inner and outer space of the nucleus. These gates are known as nuclear pores.

DNA is located in the nucleoplasm as part of chromatin, which is DNA plus other associated molecules such as histones.

The nucleus is the characteristic structure of eukaryotic cells. It contains DNA and all the molecular network to produce ARN, by a process known as transcription. Typically, cells contain only one nucleus, but there are cells with more than one, such as osteoclasts, and some cells may contain many of them as the skeletal muscle fibers or the epithelium of some invertebrates. The shape of the nucleus is variable and is usually adapted to the morphology of the cell. Typically, the nucleus is rounded, but other forms are also found, as in neutrophils which contain multi-lobulated nucleus. The localization of the nucleus is normally in the center of the cell, but it can also be found in more peripheral locations. For example, secretory cells have their nucleus located in the basal part, and skeletal muscle fibers have their nuclei close to plasma membrane.


The size and shape of the nucleus depends on the cell type, despite that all the nuclei of an individual contain the same amount of DNA. Neurons and glia are shown in this figure. Nuclei of neurons contain more loose chromatin, whereas glia nuclei show highly condensed chromatin, and therefore the size is much smaller.

Although the amount of DNA is almost the same in the nucleus of all the cells of an organism, the size of the nucleus is variable depending on the cell type. Furthermore, cells from species with different amount of DNA may show a similar nuclear size. These data indicate that the size of the nucleus is adapted to the size of the cell or to the cellular physiology, and does not directly depends on the amount of DNA.


Different nuclear shapes. A. Epithelial cells from human gall bladder with round to elongated nuclei . B. Monocyte from blood smear showing a kidney-shaped nucleus. C. Neutrophils from blood smear containing a multi-lobulated nucleus. D. Longitudinal view of a skeletal muscle fiber with many nuclei, all of them located toward the periphery (arrows).

Morphologically, there are two nuclear compartments: nuclear envelope and nucleoplasm. Nuclear envelope is the peripheral part of the nucleus that separates the interior of the nucleus, known as nucleoplasm, from the cytoplasm. Nucleoplasm-cytoplasm communication is regulated by nuclear pores, which are molecular complexes inserted in the nuclear envelope. In the nucleoplasm, DNA and associated proteins form the chromatin, which is referred as heterochromatin if it is highly condensed, or as euchromatin if it is loosely packaged. Heterochromatin and euchromatin are found in the same nucelus and the proportion of every of them depends on the type and physiological state of the cell. The nucleolus, a unique chromatin domain, is also found in the nucleoplasm, as well as other dense structures known as nuclear bodies, which are composed of chromatin and other proteins.

Here, we could go into all the molecular processes involved in DNA transcription and replication, as well as gene regulation. In the future, a new section may be opened to deal with these topics. For now, we will be focused in other features of the nuclear morphology and physiology, and encourage the reader to visit other excellent sites related to genetics.


Edens LJ, White KH, Jevtic P, Li X, Levy DL. Nuclear size regulation: from single cells to development and disease. 2013. Trends in cell biology 23:151-159.

Guo T, Fang Y. . Functional organization and dynamics of the cell nucleus. 2014. Frontiers in plant biology. vol 5. Artículo 378. doi: 10.3389/fpls.2014.00378

« Cell junctions Nuclear envelope »

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Updated: 2018-01-28. 15:16