Nucleoid: Definition and Function

Nucleoid Definition

The nucleoid is the space within a prokaryotic cell where the genetic information, called the genophore, is found. Prokaryotes are divided into bacteria and archaea, which are both unicellular organisms that contain no membrane-bound organelles. The nucleoid, then, also has no membrane around it. It attached to the cell membrane and in immediate contact with the cytoplasm. The nucleoid also doesn’t take a uniform shape and has no specific size. However, we can still distinguish it from the rest of the cell and identify it under a light microscope.

The nucleoid is mostly composed of multiple compacted copies of DNA in a continuous thread, with the addition of some RNA and proteins. The DNA in prokaryotes is double-stranded and generally takes a circular shape. Keep in mind that DNA can sometimes also be found in other regions outside the nucleoid. To put things into perspective, we can look at the nucleoid’s eukaryotic counterpart. Eukaryotes, such as plants and animals, have a nucleus that houses their genetic material, with a surrounding double membrane, or what we call the nuclear envelope. This membrane separates the contents of the nucleus from the cytoplasm. As in prokaryotes, the DNA of eukaryotes is also double-stranded.

Function of Nucleoid

The nucleoid is essential for controlling the activity of the cell and reproduction. It is where transcription and replication of DNA take place. Within it, we can expect to find enzymes that serve as biological catalysts and help with replication, as well as other proteins that have other functional and structural roles, including assisting the formation of DNA, facilitating cell growth, and regulating the genetic material of the cell.