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Definition: nucleus from Philip's Encyclopedia

In biology, membrane-bound structure that, in most cells, contains the chromosomes. As well as holding the genetic material, the nucleus is essential for the maintenance of cell processes. It manufactures the RNA used to build ribosomes. Other RNA molecules carry the genetic code from the DNA through pores in the nuclear membrane into the jelly-like cytoplasm, where it is used as a template for protein synthesis by the ribosomes. Cell division involves the splitting of the nucleus and cytoplasm. Cells without nuclei include bacteria and mammalian erythrocytes (red blood cells).

Summary Article: nucleus
from The Hutchinson Unabridged Encyclopedia with Atlas and Weather Guide

In biology, the central, membrane-enclosed part of a eukaryotic cell, containing threads of DNA. It is found in both plant and animal cells. During cell division the threads of DNA coil up to form chromosomes. The nucleus controls the function of the cell by determining which proteins are produced within it. It is where inherited information (see inheritance) is stored as genes. Because proteins are the chief structural molecules of living matter and, as enzymes, regulate all aspects of metabolism, it may be seen that the genetic code within the nucleus is effectively responsible for building and controlling the whole organism.

The nucleus contains the nucleolus, the part of the cell where ribosomes are produced. Movement of molecules into and out of the nucleus occurs through the nuclear pores. An average mammalian nucleus has approximately 3,000 pores.


Function of cell structures


Cell Structures and Functions

Cellular Organization


cell structure



inside the human body

RNA and protein synthesis

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