The Nucleus!

The nucleus is the eukaryote's equivalent of the human brain. It contains the cell's genetic information, and controls many of the cell's functions. Only eukaryotic cells have nuclei. Generally, cells will have only one nucleus; however, some cells has many nuclei--such as slime-molds or muscle cells. A prokaryotic cell does not have a nucleus, and the genetic information is dispersed throughout the cytoplasm.
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  • Bounded by the nuclear envelope (double membrane)
  • Contains chromatin
  • Commonly the most prominent organelle of the cell
  • Is highly specialized
  • Contains nucleoplasm
  • Contains the cell's hereditary material (DNA)
  • Coordinates the cell's activities (growth, metabolism, protein synthesis, and reproduction [cell division])

Nuclear Envelope
The nuclear envelope separates the contents of the nucleus from the rest of the cell. The nuclear envelope also contains holes called nuclear pores. The nuclear pores regulate the passage of specific molecules into and out of the nucleus. The nuclear envelope is also attached to the endoplasmic reticulum, which is the site of the ribosomes that play a role in protein synthesis. The nuclear envelope disintegrates during mitosis, but is reformed after cell division as the chromatin begins to unravel and disperse.
Nucleoplasm and Chromatin
Inside the nucleus, the semi-fluid substance known as nucleoplasm consists chiefly of chromatin, the less condensed form of the cell's DNA that is twisted up into structures called chromosomes during mitosis, or cell division. The chromatin is made up of DNA, the genetic material of the cell. The DNA is packed in a manner so organized that each human cell contains nearly six feet of DNA on average.

The Nucleolus!

The nucleolus is a membraneless organelle whose function is to manufacture the ribosomes that aid in the production of proteins in the cell. A nucleus can contain up to four nuclei, but each species has a fixed number. The nucleolus, like the nuclear envelope, disappears temporarily during mitosis, but is reformed in each daughter cell as chromosomes are brought together into nucleolar organizing regions.