The cell nucleus is a membrane-bound structure found in eukaryotic cells. It contains the cell's genetic material, organized as DNA molecules, which carry the instructions for the cell's functions and development. The nucleus plays a crucial role in regulating gene expression and maintaining the integrity of chromosomes. Surrounding the nucleus is the nuclear envelope, a double membrane that protects the genetic material and controls the movement of substances in and out of the nucleus. Within the nucleus, there is a region called the nucleolus, where ribosomal RNA is produced, essential for protein synthesis in the cell.