What is a Nucleoid?

Brittany Stork, John Williams
  • Author
    Brittany Stork

    Brittany taught high school mathematics for two years. They have a B.S. in Biological Sciences and Secondary Mathematics Education from the University of Nebraska-Lincoln and a Ph.D. in Cellular and Molecular Biology from Baylor College of Medicine. They tutored student-athletes at University of Nebraska-Lincoln for 5 years in various math and science classes. Brittany has served as a TA for various undergraduate and graduate level biology classes. They also are a CLRA Level II certified tutor.

  • Instructor
    John Williams
Understand what the nucleoid region is, along with what it contains. Also, explore the function and structure of the nucleoid region of a prokaryotic cell. Updated: 02/26/2022

Table of Contents


Prokaryotic and Eukaryotic Cells

Every living organism, from a mighty redwood to a little ant, is made up of cells. Cells are the building blocks of life. They contain all the equipment necessary to maintain life. Some organisms are made up of millions of cells (like the redwood), while others are just a single cell. Despite the variety of life on Earth, all cells can be classified as either prokaryotic or eukaryotic. Prokaryotic cells lack structures referred to as membrane-bound organelles. This includes a nucleus. Eukaryotic cells, on the other hand, contain many membrane-bound organelles, one of which is the nucleus.

The nucleus is the organelle that contains most of the DNA in a eukaryotic cell. DNA is the molecule that holds all the instructions needed for cell survival. Instead of a nucleus, prokaryotes have a region referred to as the nucleoid. The prokaryotic cell nucleoid houses the DNA of the cell. Why do prokaryotes have a nucleoid instead of a nucleus? Prokaryotic cells are more ancient than eukaryotic cells and did not evolve to have membrane-bound organelles. The DNA in a prokaryotic cell is still localized to a specific region; it is just not contained in an organelle.

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Nucleoid Region

The nucleoid region is a membrane-less region in the prokaryotic cell where most, if not all, of the DNA in the cell is located. The nucleoid is located directly in the cytoplasm, allowing the DNA to be n contact with the cell membrane. The DNA in prokaryotes is circular and is referred to as a plasmid. There may be multiple copies of DNA located in the nucleoid, which is not a trait shared by the eukaryotic nucleus. Given that the nucleoid definition highlights the lack of a membrane surrounding the region, it indicates that the bounds of this region are not well-defined. Although the region is irregularly shaped, it still maintains a high level of organization.

Prokaryotic cells lack a membrane-bound nucleus. The DNA of a prokaryote is located in the nucleoid region, which lacks a membrane.

Image of a prokaryotic cell.

The nucleoid region of a prokaryotic cell may also contain proteins, including various enzymes, as well as RNA (ribonucleic acid). One group of proteins called histones is one of the factors that keep the nucleoid region organized. DNA is wrapped around histones to maintain order and condense the DNA so that it takes up less space. Other proteins, including the enzyme topoisomerase, are responsible for the reverse process. During DNA replication, topoisomerases make nicks in the DNA to resolve the supercoiling as the DNA is unwound. Topoisomerases are also involved in transcription. Transcription is the process where RNA is synthesized using DNA as a template. This explains why RNA is also found in the nucleoid region.

Nucleoid Function

Now that the contents of the nucleoid are known, it is now time to investigate the function. The nucleoid functions much like the nucleus in eukaryotic cells in that it is the regulatory center of the prokaryotic cell. This region regulates the growth, reproduction, and function of the prokaryotic cell. The previously-mentioned proteins and enzymes are essential in these processes. DNA replication and RNA transcription are two processes that are essential to ensuring the cell can carry out all the activities associated with these processes.

For example, DNA synthesis is needed for the prokaryotic cells to reproduce. Bacterial cells reproduce through a process known as fission where two new cells are formed by the cell pinching in half. The fact that the DNA is associated with the cell membrane ensures that at least one copy of DNA segregates to each new cell. The transcription of RNA is another essential process because RNA provides the template for all protein synthesis. Without RNA, there would be no proteins or enzymes.

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Frequently Asked Questions

What is the nucleoid region made of?

The nucleoid region is found in the cytoplasm of prokaryotic cells. It contains DNA, sometimes several copies of it, along with proteins, including enzymes, and RNA.

What is the function of the nucleoid region?

The function of the nucleoid region is to regulate the activity of the cell. It regulates processes involved in growth, reproduction, and general cell maintenance.

Why do prokaryotes have a nucleoid region?

Prokaryotes have a nucleoid region because they lack membrane-bound organelles. Prokaryotes do not have membrane-bound organelles because they are more ancient than eukaryotes and did not evolve to have them.

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