 Cell nuclei contain most of the cell 's genetic material , organized as multiple long linear DNA molecules in complex with a large variety of proteins , such as histones , to form chromosomes . The genes within these chromosomes are the cell 's nuclear genome and are structured in such a way to promote cell function . The nucleus maintains the integrity of genes and controls the activities of the cell by regulating gene expression — the nucleus is , therefore , the control center of the cell . The main structures making up the nucleus are the nuclear envelope , a double membrane that encloses the entire organelle and <unk> its contents from the cellular cytoplasm , and the nuclear matrix ( which includes the nuclear lamina ) , a network within the nucleus that adds mechanical support , much like the cytoskeleton , which supports the cell as a whole . 
