Cell nucleus

In cell biology, the nucleus is an organelle, found in most eukaryotic cells, which contains most of the cell's genetic material. Nuclei have two primary functions:

to control chemical reactions within the cytoplasm
to store information needed for cellular division

Structure

It is surrounded by a double membrane forming the nuclear envelope, about 30 nm wide. This selectively allows molecules to enter and leave the nucleus, and separates chemical reactions taking place in cytoplasm from reactions happening within the nucleus. The outer membrane has ribosomes. The inner and outer membrane fuse at regular spaces, forming nuclear pores.

The nucleus contains the nucleolus and a fibrous matrix.

The outer membrane is continuous with the rough endoplasmic reticulum (RER). The space between the two membranes is continuous with the lumen of the RER.

Similar to the cytoplasm of a cell, the nucleus contains nucleoplasm - a highly viscous solid containing the chromosomes and nucleoli. Chromosomes contain information encoded in DNA attached to proteins called histones and are usually arranged into a dense network called chromatin. Nucleoli are granular structures which make ribonucleic DNA (rDNA) and assemble it with proteins.

Details

The nucleus, being the largest sub-cellular compartment, varies in diameter from 10 to 20 micrometres.