Nucleoid

The irregular, non-membrane-bound region of a prokaryotic cell where its chromosome is concentrated. Its DNA is organized by supercoiling and proteins rather than enclosed in a nucleus.

DNA supercoiling: The over- or under-winding of DNA relative to its relaxed helical state. Supercoiling compacts chromosome DNA and helps organize it within the nucleoid.
Prokaryote: An organism whose cells lack a membrane-bound nucleus. Prokaryotic cells contain nucleoids instead of nuclei.
Bacterial cell division: The process by which a bacterium grows and divides into daughter cells. Chromosome organization in the nucleoid affects DNA segregation during division.
Anton van Leeuwenhoek: A Dutch microscopist who made early observations of microorganisms in the seventeenth century. His observations established microscopy as a way to study bacterial cells, though not nucleoid structure.
Nucleoid-associated proteins: Proteins that bind bacterial DNA and influence its structure, accessibility, and organization. These proteins bend, bridge, or constrain DNA to help shape the nucleoid.
Nucleus: A membrane-bound organelle that houses most of a eukaryotic cell’s genetic material. Unlike a nucleus, the nucleoid has no surrounding membrane.
DNA replication: The process by which a cell copies its DNA before division. Replication begins and proceeds on the chromosome organized in the nucleoid.
Light microscopy: Imaging that uses visible light and lenses to resolve small objects. Light microscopy first revealed stained chromosome-containing regions in bacterial cells.
Chromosome conformation capture: A family of methods that detects physical contacts between distant regions of DNA. Contact maps reveal the chromosome’s spatial organization inside the nucleoid.
Eukaryote: An organism whose cells contain a membrane-bound nucleus and other internal compartments. Eukaryotic chromosomes are enclosed in nuclei rather than concentrated in nucleoids.

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