The cell nucleus is the most prominent part of the cell. It is derived from Latin word nucleus which means ‘kernel’. It is a highly specialized organelle of the cell. It constitutes most of the genetic material of the cell and coordinates the activities of the cell like growth, metabolism, and cell division. Almost all eukaryotic cells contain nucleus except red blood cells. It regulates the activities of the cell so it is called control center of the cell. Usually, there is only one nucleus in the cell but a few exceptions are there like slime molds and Siphonales which have more than one. It covers almost 10% of the total volume of the cell. Structure and function of the cell nucleus are described below.
Structure of the Cell Nucleus
The nucleus is filled with a viscous fluid called nucleoplasm. Other prominent parts of the nucleus include the nuclear envelope, nuclear pores, chromosomes, and nucleolus.
The nuclear envelope is made up of two membranes: the outer membrane and the inner membrane. The out membrane is continuous with the membrane of the rough endoplasmic reticulum. There is a little space between these two layers called the perinuclear space. The function of the nuclear envelope is to enclose the genetic material and keep it separated from the cytoplasm as well as acts as a barrier between the cytoplasm and nucleoplasm to prevent passage of macro-molecules.
The nuclear envelope is perforated with many tiny pores called nuclear pores made up of numerous proteins called nucleoproteins. The regulate the entry and exit of molecules (only about 9 mm wide) between cytoplasm and the nucleus. Molecules larger than this are transported by the mechanism of active transport.
The nucleus contains most of the genetic material of the cell in the form of linear DNA molecules. The DNA is organized in the form of chromosomes. Chromosomes are the threadlike structures found in the nucleus of almost all organisms. Chromosomes are made up of protein and DNA. Every species has a specific number of chromosomes in their nucleus. Chromosomes are invisible under the microscope if a cell is in the non-dividing state but when cell the cell is going to divide the chromatin forms well-defined chromosomes. The DNA on the chromosomes contains complete genome of the cell. However, mitochondria also contain some genes.
The nucleolus is a densely stained structure found in the nucleus. It is the largest structure in the nuclei of eukaryotic cells. It is the site of ribosome synthesis and assembly. Other functions include transporting molecules, vital substances, and ions to ensure efficient cell metabolism. It made up of protein and RNA. It synthesizes and assembles ribosomal RNA. During cell division, the nucleolus disappears.
Function of the Cell Nucleus
The cell nucleus contains the hereditary information of the cell. Protein synthesis, cell division, growth and differentiation all occur in the nucleus. Its main function is to control gene expression and mediate the DNA replication during the cell cycle. It also aids in the exchange of RNA and DNA and between nucleus and cytoplasm. It is the site for Transcription and Translation processes in which mRNA and proteins are made respectively.