Flexi Says: Most of the eukaryotic cells have a nucleus. The nucleus is where cells store their DNA, which is the genetic material. Essentially, the nucleus is the control center of the cell. The function of the nucleus is to maintain the integrity of the genes and to control the activities of the cell by regulating gene expression. Without nucleus cells loose the capacity of cell division and they will be short lived with very specific functions. For example Mature red blood cells do not have a nucleus or other organelles. Lacking these components allows the cells to have more hemoglobin and carry more oxygen.