The eukaryotic nucleus is defined as a double-membrane-bound organelle whose primary function is to contain and compartmentalize the cell's chromosomal DNA, separating the nucleoplasm from the cytoplasm by a nuclear envelope comprising an outer membrane, an inner membrane, and the nuclear pore complexes that span both. Because compartmentalization would otherwise prohibit exchange, selective bidirectional transport — mRNA and assembled ribosomal subunits outward, proteins such as polymerases inward — occurs exclusively through nuclear pores, which recognize specific targeting signals borne by transported proteins. Within the nucleoplasm the nucleolus constitutes a dense, non-membrane-bound subregion enriched in DNA encoding ribosomal RNA and serving as the site of ribosome assembly; topologically, the outer nuclear membrane is continuous with the endoplasmic reticulum, making the perinuclear space continuous with the ER lumen. This concept belongs to cell biology, specifically eukaryotic organelle structure–function, and grounds the broader principle that membrane compartmentalization plus regulated transport defines eukaryotic cellular organization.
The eukaryotic nucleus is defined as a double-membrane-bound organelle whose primary function is to contain and compartmentalize the cell's chromosomal DNA, separating the nucleoplasm from the cytopl…