(Visit the University of Texas - Medical Branch for a throughly illustrated lecture on the nucleus)
When stained the nucleus is the most salient feature of a cell. This prominent organelle has dual functions:
Most of the cells DNA resides in the nucleus. The DNA combines with a variety of proteins to form linear molecules called chromosomes The chromosome may be functionally divided into a number of hereditary units called genes.
Chromosomes, literally color bodies, are so named because they are easily stained by a number of pigments.
A diagram of four nucleotide pairs of DNA's double molecular structure is shown below.
Within the nucleus are the nucleoli darkly stained bodies involved in intense RNA synthesis. This is where ribosomes are formed in a eukaryotic cell.
When a cell is ready to divide chromosomes become visible using a light microscope because they thicken due to a highly coiled state.
The nucleus has a double membrane surrounding it called the nuclear envelope.
Scattered generously throughout the nuclear membrane are openings called nuclear pores which allow materials to pass back and forth between the nucleus and the cytoplasm. The nuclear pores are a complex of 8 adjoining proteins which form a circular cluster often seen with a central plug. Take a look at a freeze-fracture preparation of nuclear pores.
Click on individual labels in the diagram for electron micrographs and further explanation
Modified July 9, 2005