NUCLEUS

The interphase ( non dividing cell phase) nucleus has highly extended and elaborate nucleoprotein fibres called chromatin, nuclear matrix and one or more spherical bodies called nucleoli.
The nuclear envelope consists of two parallel membranes with a space between them called the perinuclear space.
At a number of places, the nuclear envelope is interrupted by minute pores, which are formed by the fusion of its two membranes.
nuclear matrix --nucleoplasm
The nucleoli are spherical structures present in the nucleoplasm.
Nucleolus is the site of active ribosomal RNA (rRNA) synthesis.

A loose and indistinct network of nucleoprotein fibres is called chromatin.
During different stages of cell division, cells show structured chromosomes in place of the nucleus.
Chromatin contains DNA and some basic proteins called histones, some non-histone proteins and also RNA.

Every chromosome -- a primary constriction or the centromere on the sides of which disc shaped structures called kinetochore are present.

Based on the position of the centromere, the chromosomes can be classified into four types
Metacentric
Submetacentric
Acrocentric
Telocentric

The metacentric chromosome has middle centromere -- two equal arms of the chromosome.
The sub-metacentric chromosome has centromere nearer to one end of the chromosome -- one shorter arm and one longer arm.
In case of acrocentric chromosome, the centromere is situated close to its end -- one extremely short and one very long arm
telocentric chromosome -- terminal centromere.

Sometimes a few chromosomes have non-staining secondary constrictions, which gives the appearance of a small fragment called the satellite - SAT CHROMOSOME.

MICROBODIES

Many membrane bound minute vesicles are called microbodies.
Microbodies contain various enzymes, are present in both plant and animal cells.