Cell nucleus

A membrane-bound organelle in eukaryotic cells that contains most of the cell’s DNA and helps regulate gene expression.

Nuclear envelope: The double membrane surrounding the nucleus, continuous with the endoplasmic reticulum. It separates nuclear contents from the cytoplasm while connecting the nucleus to cellular membranes.
Eukaryote: An organism whose cells contain a nucleus and other membrane-bound organelles. The nucleus is a defining feature of eukaryotic cell organization.
Eukaryogenesis: The evolutionary emergence of eukaryotic cells from earlier cellular ancestors. The origin of the nucleus is a central part of explaining how eukaryotic cells arose.
Prokaryote: An organism whose cells lack a membrane-bound nucleus. Prokaryotic DNA is not enclosed by the defining membrane-bound compartment of eukaryotes.
Nuclear pore complex: A large protein assembly embedded in the nuclear envelope that regulates transport between nucleus and cytoplasm. It controls which proteins and RNA molecules cross the nuclear envelope.
DNA: The molecule that stores hereditary information in most organisms. Most cellular DNA is housed and maintained inside the nucleus.
Lynn Margulis: An American biologist who advanced the modern theory of endosymbiosis. Her work reshaped accounts of eukaryotic origins, though endosymbiosis does not by itself explain the nucleus.
Nucleoid: The irregular region in a prokaryotic cell where its chromosome is concentrated. It organizes DNA without the nuclear envelope that encloses eukaryotic genomes.
Chromatin: The complex of DNA and associated proteins that packages eukaryotic genomes. Chromatin organizes the DNA housed in the nucleus and influences its accessibility.
Gene expression: The processes by which information in a gene produces a functional RNA or protein. The nucleus regulates access to genes and the production of their RNA.

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