Nukleoidi

Nukleoidi are the region of prokaryotic cells in which most of the genetic material is located. They are not enclosed by a membrane and are found in the cytoplasm as a compact, irregular mass that contains the chromosome, plasmids in some species, and a set of DNA-binding and DNA-modifying proteins. In bacteria and archaea, the nucleoid serves as the functional equivalent of the eukaryotic nucleus, organizing genetic information for replication, transcription, and segregation during cell division.

The organization of the nucleoid arises from a combination of DNA supercoiling, macromolecular crowding, and interactions with nucleoid-associated proteins. These proteins bind to DNA to bend, bridge, or wrap the molecule, creating loop domains that compact the genome without fully separating it from the cytoplasmic environment. Enzymes such as DNA gyrase and topoisomerases regulate DNA supercoiling, while structural maintenance of chromosomes (SMC) complexes contribute to condensation and sister chromatid separation. In many bacteria, cytoskeletal elements influence nucleoid positioning and dynamics within the cell.

Nucleoid structure is dynamic and changes with growth conditions, cell cycle stage, and replication status. During replication, newly synthesized DNA is organized and partitioned so that daughter cells receive genetic material. The nucleoid also affects gene expression patterns through its physical organization, which can influence promoter accessibility and transcriptional activity.

Across domains, nucleoids share the common feature of housing genetic material without a surrounding membrane, though the specific organizing proteins differ. In mitochondria and some plastids, nucleoid-like structures exist as circular genomes packaged with distinct proteins. Overall, the nucleoid is essential for maintaining genome integrity, regulating access to genetic information, and ensuring proper genome distribution during cell division.