The nucleus is the control center of the cell. Therefore, it may be the most important organelle.
The nucleus is wrapped with a double-layered membranes. The inner mass of material is called the karyoplasm.
The karyoplasm is a fluid containing the solution of chromatin. Chromatin is the complex of DNA and the protein, histone. It is believed that DNA threads are winding on granules of histones.
Then, the structure is called the nucleosomes. So, the chromatin looks like the thread of DNA chaining the beads of nucleosomes.
Chain of nucleosomes wound with DNA
At normal time, the threads of DNA are spreading throughout the whole nucleus. So, it does not have any shape and cannot be distinguished from any other structure.
When the cell is about to divide, the chromatin would condense and heavily packed. Then, they gain the shapes and called the chromosomes.
The DNA is responsible for transmitting inheritance message to RNA for the production of proteins. Therefore, it is believed that RNA is produced in nucleus. There may be one or two area condensed with RNA.
These structures are called nucleoli (nucleolus in singular form).
It is believed that the main function of the nucleolus is for the storage of RNA. When the specific RNA is in need, it would be sent out for the production of the specific protein.
The following is the electronmicrograph of the nucleus of a liver cell.
