The nucleus can be thought of as the control center of a eukaryotic cell because it contains most of the genetic material that carries the instructions for the cell's operations. Inside the nucleus, DNA directs the sequence of chemical steps needed for the synthesis of proteins and, by way of the proteins' action, it controls the metabolism of the rest of the cell.
Inside the cell's nucleus rests a long molecule called DNA. This strand of genetic material contains the instructions needed to build a body, influence its behavior and drive the chemistry of the cell itself. These instructions are coded as a sequence of nucleotides called genes that can be read by single strands of nucleotides called messenger RNA. Messenger RNA reads off the sequence of instructions coded in the DNA, alters its shape in response to the exact sequence it has read and passes out of the nucleus to instruct the cell's internal machinery in the steps needed to synthesize proteins. Some of these proteins help digest food, some build or destroy other proteins and some are useful in transporting chemicals through the wall of the cell. Very nearly every action the cell takes is in some way influenced by the DNA of the nucleus.