nucleóide

The nucleoid is the irregular, non-membrane-bound region of prokaryotic cells where the genetic material is localized. In bacteria and archaea, the chromosome is typically a circular DNA molecule that occupies this region; there is no surrounding nuclear envelope as in eukaryotic cells.

DNA in the nucleoid is highly compacted through supercoiling and the formation of looped domains. This organization is mediated by nucleoid-associated proteins (NAPs) such as HU, IHF, Fis, and H-NS in bacteria, and analogous histone-like proteins in archaea. Structural maintenance of chromosomes (SMC) family proteins and topoisomerases also contribute to condensation and topology.

Replication and transcription occur within the nucleoid, and the processes of gene expression influence and are influenced by DNA topology. The nucleoid contains the primary chromosome and, in many species, plasmids. Chromosome segregation during cell division is coordinated with nucleoid organization.

Size and shape of the nucleoid vary with growth conditions and cell cycle stage. In addition to bacteria and archaea, the term nucleoid is also used to describe the DNA-protein complexes inside organelles such as mitochondria and chloroplasts, where DNA is organized with organelle-specific proteins (for example, TFAM in mitochondria).

Compared with the nucleus of eukaryotic cells, the nucleoid is not bounded by a membrane, reflecting the fundamental difference between prokaryotic and eukaryotic cellular organization.