The nucleus is the 'brain' of a eukaryotic cell and controls all the activities of the cell. It contains most of the genetic information of the cell, in the form of DNA molecules, and is enclosed within a membrane, the nuclear membrane. The main function of the nucleus is to regulate gene expression, protect genetic material and replicate genetic material during cell division. The nucleus provides the location for gene transcription, isolated from the cytoplasm. This allows eukaryotic organisms higher levels of genetic regulation as compared to prokaryotic cells. The nuclear membrane allows for selective transport between the cytoplasm and the nucleus, using pores in the membrane. This also allows the nucleus to maintain the integrity of the genetic material.