Nucleus is double membrane bound organelle present at center of cells. The nucleus holds the cell's DNA and controls all cell function. Cells with a nucleus are eukaryotic, and are also known as eukaryotes. The nuclear envelope in eukaryotes is like our skull, covering the nucleus and keeping the DNA safe.
This organelle has two major functions: it stores the cell's hereditary material, or DNA, and it coordinates the cell's activities, which include growth, intermediary metabolism, protein synthesis, and reproduction (cell division). Only the cells of advanced organisms, known as eukaryotes, have a nucleus.