The term nucleus (plural nuclei) comes from the Latin word nuculeus which means kernel. It is a membrane-enclosed organelle that is found in eukaryotic cells and contains most of the genetic materials of the cell, which are organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, in order to form chromosomes. The genes found within these chromosomes are the cells' nuclear genome. The nucleus is also referred to as the control center of the cell, wherein movement, reproduction and eating are being controlled. Although it is not commonly located in the center of the cell, it is basically a big dark spot found in the middle of the cytoplasm (cytosol), which is the fluid that fills the cells.
Nucleus Function and Structure
The main nucleus function is to maintain the integrity of the genes as well as to control the cells activities by means of gene expression regulation, which makes the nucleus as the control center of the cell.
The main structures that make up the nucleus are the nuclear envelope, which is a double membrane that separates and encloses the entire organelle and its contents from the cellular cytoplasm; and the nucleoskeleton, which is a meshwork found in the nucleus that adds mechanical support, like the cytoskeleton, and supports the cell as a whole. Nucleoskeleton also includes the nuclear lamina.
Since the nuclear membrane is impermeable (not permitting the passage of fluid, gas and other substances) to most molecules, nuclear pores are present to allow the movement of molecules across the envelope. Such pores cross both of the membranes and provide a channel that is allowing free movement of ions and small molecules. The movement of proteins and other larger molecules are carefully controlled as it requires active transport regulated by carrier proteins. The micro-nuclear transport is essential to maintain the function of the cell, as movement through the pores is needed for both chromosomal maintenance and gene expression.