The nucleus of a plant or animal cell is made of chromatin and nucleoli. Chromatin is made of DNA and protein, and nucleoli are small bodies that hold protein and RNA. The nucleus of an atom contains neutrons and protons, unless it's a hydrogen nucleus, which only contains one proton.
The nucleus of a cell is sometimes found near its center. A membrane surrounds it and separates it from the cytoplasm of the cell. The DNA that makes up part of the nucleus' chromatin is an enormous molecule that controls the living being's heredity. It does this by controlling the actions of proteins. DNA makes the instructions for every type of protein in the cell. These proteins are created in the cell's cytoplasm. They include enzymes that regulate chemical reactions in the cell. Though many chemical reactions can occur without enzymes, the enzymes speed them up. Other chemical reactions couldn't occur at all without enzymes.
RNA is much like DNA, except it's found in the cytoplasm as well as the nucleus. DNA never leaves the nucleus. So, when a protein needs to be made, RNA copies the instructions DNA made for the protein's manufacture. It then leaves the nucleus and goes to the places in the cell where proteins are made.