A cell is the basic unit of life. In majority cells, there are certain components known as the organelles. One of the organelles is the nucleus. The nucleus acts as the control center of the cell because nucleus functions to control all the movements of the cell. The nucleus contains the genetic information encoded in DNA of chromosome. It also directs protein synthesis by synthesizing messenger RNA (mRNA) and sending it to the cytoplasm via the nuclear pores. The nucleus consists of 4 components:
a) chromatin organized as euchromatin and heterochromatin
b) nucleolus
c) membranous nuclear envelope with the fibrous lamina
d) nucleoplasm
In most cells, chromatins have homogenous appearance clumps of densely staining. Stained chromatin usually appears through both light microscopes and electron microscopes. Chromatins are embedded in among lightly staining background. The densely stained material is highly condensed chromatin called heterochromatin. It is basophilic component. The lightly stained component is dispersed form called euchromatin. It is not recognized with the light microscope. The euchromatin is an indicative of active chromatin because its genetic information can be transcribed. It is prominent in cell with increasing level of metabolic activity such as neurons, liver cells. Protein of chromatin includes some basic protein histone and some others called non-histone protein.
Nucleolus is a non membranous structure form by granular and filamental materials. It varies in size, particularly well developed in cells, and active in protein synthesis. The nucleolus largely composed RNA and proteins. It is responsible for ribosomal RNA synthesis. Some nuclei can contain more than one nucleolus. Like chromatin, nucleoli are also basophilic.
Nuclear envelope consists of 2 parallel membrane. The 2 membranes, each a lipid bilayer with associated proteins, are separated about 20-40nm from each other by perinuclear space. The perinuclear space is connected with the space of rough endoplasmic reticulum (RER). Ribosomes are often present in the cytoplasmic site of the nuclear envelope. The inner membrane of nuclear envelope contains thin, additional, electron dense protein layer called the fibrous or nuclear lamina. Nuclear lamina is the specialized type of intermediate filament. The nuclear envelope is perforated by pores called nuclear pores.
The nuclear pore looks like membrane bounded octagonal channel between nucleus and cytoplasm. At the lip of each pore, the inner and outer membranes of the nuclear envelope are fused. An intricate protein structure called a pore complex lines each pore and regulates the entry and exit of certain large macromolecules and particles.
The nucleoplasm is a highly viscous liquid that surrounds the chromosomes and nucleoli. It serves as the medium for transparent chemical and structural component of nucleus. Many substances such as nucleotide (necessary for purposes such as the replication of DNA) and enzyme (which direct activities that take place in the nucleus) are dissolved in the nucleoplasm. A network of fibers known as the nuclear matrix can also be found in the nucleoplasm extending throughout the nuclear interior. The soluble, liquid portion of the nucleoplasm is called the nuclear hyaloplasm.
