Nucleus. The nucleus is the control centre of the living cell and it contains more than 95% of the cell's DNA. A double-membrane structure called the nuclear envelope, embedded with nuclear pores, separates the nucleus from the cytosol.

The nucleolus, dense mass, is the major site of RNA synthesis and is the site where ribosome subunits are assembled.

DNA in the nucleus is coiled into supperstructure units known as chromosomes which are in turn assembled into a dense mass called chromatine.

Transcription of the DNA into RNA is the first step in the expression of the genetic information (encoded in the DNA) and is the major metabolic activity of the nucleus.

 

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