The cell nucleus acts like brain of the cell. It helps control eating, in movement and reproduction. If anything of them happens in the cell, chances are that nucleus knows about it. It is not necessary for the nucleus to be in the center of the cell. It can be spotted as a big dark spot somewhere in middle of all the cytoplasm (cytosol). One will not probably find it near the edge of cell because that might be dangerous.
Not all cells have their nucleus. Biology breaks the cell types into eukaryotic and prokaryotic. Eukaryotic cells have well defined nucleus while prokaryotic ones have no defined nucleus. There is no need for having a nucleus to have DNA. If the cell have not any nucleus, its DNA probably found floating around the cell in a region called as nucleoid. A defined nucleus that holds down the genetic code is an advanced feature of the cell.
Important Materials in Nuclear Envelope
Nucleus is the largest organelle in eukaryotic cells. It is surrounded by two membranes. Each one is a phospholipid bilayer consist of different types of proteins. Inner nuclear membrane defines nucleus. Outer membrane of nucleus is continuous with rough Endoplasmic reticulum(ER) and the space between inner and outer nuclear membrane is continuous with the lumen of rough ER.
The things that make the eukaryotic cell are a defined nucleus and some other organelles. The nuclear envelope surrounds the nucleus and all its contents. Nuclear envelope is a membrane similar to cell membrane around the entire cell. There are pores and spaces for proteins and RNA to pass through while nuclear envelope keeps all of the nucleolus and chromatin inside.
When the cell is in resting state, then there is something known as chromatin in the nucleus. Chromatin is made up of RNA, DNA and nuclear proteins. RNA and DNA are the nucleic acids inside the cell. When a cell is about to divide, the chromatin suddenly becomes very compact, i.e. it condenses. When these chromatin comes together, chromosomes can be seen. Nucleolus can also be find inside the nucleus. It is made up of protein and RNA. It does not contains much DNA at all.
Two nuclear membranes appear to fuse at nucleopores. These ring like pores are made of specific membrane proteins and acts like channels that regulates the movement of substances between nucleus and cytosol.
In growing or differentiating cell, nucleus is metabolically active that produce DNA and RNA.These RNA is exported to the cytoplasm to involve in protein synthesis. In “resting cells” the production of DNA and RNA are minimal. In nucleus which is non-dividing, the chromosomes are dispersed cannot be seen through light microscope because of lack in thickness. Only during cell division the chromosomes becomes visible under light microscope. Chromosomes forms the basic heredity. Genes which are the chemical basis of heredity are arranged in linear fashion on the chromosomes. Nuleolus, a sub organelle of nucleus is easily seen through light microscope.Most of ribosomal RNA are produced in nucleolus. Finished or partially finished ribosomal subunits pass through nucleopores to reach cytosol.
Non-nucleolar region of nucleus called as Nucleoplasm. It has very high DNA concentration. Fibrous proteins called Lamins form a two dimensional network along the inner surface of the inner membrane giving shape and apparently binding DNA to it. During the early stages of cell division breakdown of this network occurs.
Function of Nucleus :
- Controls all metabolic activities of the cell by controlling the synthesis of enzymes required.
- It controls the inheritance of characters from parents to offsprings.
- Controls cell division.