The nucleus of the cell controls all cell activities. It contains the bulk of the genetic material and acts as the brain of the cell. The nucleus makes up about 10 percent of a cell's total volume.
The two major parts of the nucleus are the nucleolus and the chromatin, which contains the DNA. A strand of DNA is almost 6 feet long. It is divided into 46 molecules, one for each chromosome. The nuclear envelope encloses the nuclear contents and is perforated with nuclear pores. These pores regulate which molecules are allowed to pass between the cytoplasm and the nucleus.