The NucleusThe nucleus is the control centre of the cell. It is surrounded by a nuclear envelope that is two membranes thick. The membranes have pores in them to allow materials to enter and exit (e.g. mRNA). The envelope also helps with maintaining shape.
The nucleus also contains the cell's genetic information (DNA). When the cell is not dividing, DNA is combined with histone proteins. The combination is called chromatin. On the other hand, when the cell is going to divide, DNA is twisted into coils by histone proteins; these coils are called chromosomes. Furthermore, the nucleus contains one or more nucleoli (singular: nucleolus). Ribosomal ribonucleic acid (rRNA) synthesis occurs there. The nucleus plays a major role in the cell as it can determine which proteins the cell should make. This is done by sending messenger RNA (mRNA) to signal ribosomes in the cytoplasm to make a specific protein. Remember that the genetic code which controls cell activity is located inside the nucleus. |