In this article we will discuss about the Nucleus of Controlling Centre of Cell.
The protoplast of eukaryotic cell contains prominent spherical or subspherical body called the nucleus (Pl.—nuclei) which controls all the life activities. As a rule, there is only one nucleus in one cell, but there are certain exceptions to this general rule. There may be many nuclei in syncytium which is formed by fusion of many uninucleate cells. Multinucleate cells (coenocytes) are commonly found in plants.
Coenocytic condition results due to repeated nuclear division without cytokinesis. Sieve cells (phloem) of angiosperms and mammalian red blood cells lose their nuclei during the process of maturation. The anucleated cells are incapable of growth and division. The cells of bacteria and blue-green algae do not possess organised nuclei.
The nuclei in some cells may be seen in the centre but in the majority of cells they may occur at any place in the cytoplasm. There is but little optical differentiation between the nucleus and the cytoplasm.
The following are the principal components of the interphase nucleus (Fig. 1.26):
(a) Nuclear envelope,
(b) Nuclear sap,
(c) Nuclear reticulum or chromatic reticulum and
(a) Nuclear Envelope:
Nucleus is bounded by two membranes of lipoprotein. The nuclear membrane contains many pores or annuli through which movement of substances takes place. The outer membrane of nuclear envelope remains continuous with the membranes of endoplasmic reticulum.
(b) Nuclear Sap:
The space bounded by nuclear envelope is filled by the groundplasm, known as nucleoplasm, nuclear sap or karyolymph. The nucleoplasm contains dissolved sugars, proteins, nucleotides, nucleic acids, energy rich compounds and a variety of enzymes.
(c) Nuclear Reticulum or Chromatic Reticulum:
The nucleoplasm contains thread like elongated structures of chromatin called chromatin fibres. The chromatin fibres later on differentiate to form thread-like structures of definite shapes and sizes which are called chromosomes.
The chromatin fibres in the nucleus of a growing cell form a network type structure that is called chromatic reticulum. Chromatin is fundamentally nucleoprotein complex (Nucleic acids and proteins).
In the nucleoplasm there occurs a conspicuous body of spherical shape attached to a particular chromosome on a definite location. This is called nucleolus. Nucleolus is composed of a large amount of ribosomal proteins and ribosomal RNA and thus provides the raw materials for the biogenesis of ribosomes.