In biology, the structure in a cell that contains the chromosomes. The nucleus has a membrane around it, and is where RNA is made from the DNA in the chromosomes. Plural: nuclei1.
The part of a cell that contains the genetic material, DNA. The DNA, which is combined with protein, is normally dispersed throughout the nucleus as chromatin. During cell division the chromatin becomes visible as chromosomes. The nucleus also contains RNA, most of which is located in the nucleolus. The nucleus is separated from the cytoplasm by a double membrane, the nuclear envelope22.