Describe about nucleus in detail.

Explanation

Nucleus as a cell organelle was first described by Robert Brown in 1831. Later the material of the nucleus stained by the basic dyes was given the name chromatin by Flemming
The interphase nucleus has highly extended and elaborate nucleoprotein fibres called chromatin, nuclear matrix and one or more spherical bodies called nucleoli.
The nuclear envelope which consists of two parallel membranes with a space between (10 to 50 nm) called the perinuclear space.
This forms a barrier between the materials present inside the nucleus and that of the cytoplasm. The outer membrane usually remains continuous with the endoplasmic reticulum and also bears ribosomes on it.

At a number of places the nuclear envelope is interrupted by minute pores, which are formed by the fusion of its two membranes. These nuclear pores are the passages through which movement of RNA and protein molecules takes place in both directions between the nucleus and cytoplasm.
Nucleoli : The nucleoli are spherical structures present in the nucleoplasm. The content of nucleolus is continuous with the rest of the nucleoplasm. It is a site for active ribosomal RNA synthesis.
Large and more numerous nucleoli are present in cells actively carrying out protein synthesis.