The largest of the membrane-bounded organelles which characterize eukaryotic cells; it is thought of as the control center since it contains the bulk of the cell's genetic information in the form of deoxyribonucleic acid (DNA). The nucleus has two major functions: (1) It is the site of synthesis of ribonucleic acid (RNA), which in turn directs the formation of the protein molecules on which all life depends; and (2) in any cell preparing for division, the nucleus precisely duplicates its DNA for later distribution to cell progeny. The discovery of the nucleus dates back to 1710, when the Dutch microscopist Antonie van Leeuwenhoek noted a centrally located “clear” area in living blood cells of birds and amphibians. However, it was not until 1831 that the British botanist Robert Brown first used the term nucleus and provided a precise morphological description.