The largest organelle within a cell is the nucleus. The nucleus contains the majority of the cell's DNA and controls the cell's growth and reproduction. The nucleus is surrounded by a double membrane, called the nuclear envelope, which protects the DNA from damage. Within the nucleus are smaller structures called chromatin and nucleoli. Chromatin consists of long strands of DNA that are coiled around proteins called histones. Nucleoli are small regions where ribosomes are produced. Ribosomes are responsible for manufacturing proteins within cells.