The nucleus is a membrane-bound organelle found in eukaryotic cells that serves as the control center of the cell. It contains the cell's genetic material, organized into chromosomes, which are made of DNA. This genetic material carries the instructions necessary for the cell's growth, development, and functioning. The nucleus does not combine amino acids to make proteins; that process occurs in the ribosomes. It also does not provide energy to the cell; that function is primarily carried out by mitochondria. Additionally, while the nucleus plays a role in regulating gene expression, the control of what enters and leaves the cell is managed by the cell membrane. Therefore, the primary function of the nucleus is to store and protect the cell's genetic material.