The nucleus is the control center of the cell. It is necessary for cell division and growth. The nucleus contains the cell's DNA, which is organized into genes. Genes are responsible for directing the cell's activities, such as growth, metabolism, and reproduction. It is also responsible for reproduction, growth and development. The nucleus contains the nucleolus, which is responsible for synthesizing ribosomes. Ribosomes are responsible for protein synthesis. The nucleus also contains the nuclear envelope, which is responsible for protecting the nucleus from the rest of the cell.