Cell Nucleus – Genetic Library of the Cell
The nucleus is the brain of eukaryotic cells. It is only present in eukaryotic cells (which are eukaryotic because they have a nucleus).
The nucleus is a major, centrally located spherical cellular component. The nucleus is a highly specialized organelle that serves as the information processing and administrative center of the cell. The nucleus stores the cell's hereditary material, or DNA, it plays an important part in cell division and it controls and coordinates various life processes of the cell, which include growth, intermediary metabolism, protein synthesis.
A double–layered membrane, the nuclear envelope, separates the contents of the nucleus from the cellular cytoplasm. Nuclear envelope encloses a space between two nuclear membranes and is connected to a system of membranes called the endoplasmic reticulums (ER) where protein synthesis occurs, and is usually studded with ribosomes. The envelope contains many pores called nuclear pores and encloses a semi fluid substance called nucleoplasm. Nuclear pores allow specific types and sizes of molecules to pass back and forth between the nucleus and the cytoplasm.
Nucleus encloses life's most important molecule – DNA
Two types of nuclear structures called the nucleolus (plural: nucleoli) and chromatin material are embedded within the nucleoplasm. The nucleus may contain one nucleolus or more nucleoli. The nucleolus contains ribosomes, RNA, DNA, and proteins. The nucleolus synthesizes protein-producing macromolecular assemblies called ribosomes. Nucleolus is known as factory of ribosomes.
The chromatin material is a thin, thread–like intertwined mass of chromosomes material and composed of the genetic substance DNA (deoxyribonucleic acid) and proteins. DNA stores all the information necessary for the cell to function (i.e., metabolism), to grow and to reproduce further cells of the next generation. Segments of DNA are called genes. The chromatin is condensed into two or more thick ribbon like chromosomes during the division of cell. Each eukaryotic species has a characteristic number of chromosomes. A typical human cell, for example, has 46 chromosomes in its nucleus.