The nucleus, a large and rounded organelle, is the control center of the cell. In a cell that is not in the process of dividing, the nucleus contains loosely coiled material called chromatin. When a cell prepares to divide, the chromatin becomes more tightly coiled and condenses to form rod-shaped bodies, called the chromosomes. Each chromosomes contains hundreds or thousands of genes which are the units of hereditary information that govern the structure and activity of the cell. The genes, which are arranged in a specific linear order, are composed of the chemical compound DNA. We can think of the chromosomes as a chemical cookbook for the cell and each gene as a recipe for making a specific protein.
The complete set of genes that make up the human genetic material is the human genome. The Human Genome Project, completed in 2003, mapped the 30,000 or so genes that make up the human genome. Researches continue to study the proteins coded by the genes. Genome research is providing knowledge that can be applied to prevention and treatment of many human disorders.
The nucleolus is a specialized region within the nucleus. The nucleolus assembles ribosomes, organelles that help manufacture proteins.
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