kidzsearch.com > wiki Explore:images videos games
A cell nucleus is the part of the cell which contains the genetic code, the DNA, and the RNA. It also controls the activities in a cell. The nucleus is small and round, and it works as the cell's control center. It contains chromosomes which house the DNA. Chromosomes are more widely recognised by the shape they form during cell division. The human body contains billions of cells, which vary from blood cells that carry oxygen from one part of the body to another, nerve cells which create reactions that stimulate feelings and data, and skin cells that protect the cells underneath.
Cell nuclei are only found in eukaryotes. They were first found by Antonie van Leeuwenhoek in the 17th century. Bacteria and Archaea are single-celled organisms of quite a different type: they are prokaryotes, and their cells do not have nuclei, or membrane bound organelles. Some eukaryotes (like amoebas) consist of only one cell with the same basic materials as multi-cellular organisms.
Inside the nucleus there are no membrane-bound sub-compartments. its contents are not uniform, and a number of sub-nuclear bodies exist, made up of unique proteins, RNA molecules, and particular parts of the chromosomes. The best-known of these is the nucleolus, which is mainly involved in the assembly of ribosomes. After being produced in the nucleolus, ribosomes are exported to the cytoplasm where they translate mRNA.
Within the nucleus is a structure called a nucleolus. It is made at a nucleolus organizer region (NOR). This is a chromosomal region around which the nucleolus forms. Inside the nucleolus ribosomes are made. These are exported through the nuclear pore complexes to the cytoplasm, where they are free or become attached to the endoplasmic reticulum, forming rough endoplasmic reticulum (RER).
Large molecules cannot get through the double-layer nuclear membrane: it is impermeable to them. However, nuclear pores exist. They control the movement of molecules across the membrane. The pores cross both nuclear membranes, providing a channel. The larger molecules are actively transported by carrier proteins, and there is free movement of small molecules and ions. Movement of large molecules such as proteins and RNA through the pores is required for both gene expression and the maintenance of chromosomes.
- Cooper, Geoffrey M.; Hausman, Robert E. (2007). The Cell: a molecular approach (4th ed.). Sinauer Associates. pp. 371–9. .