Chromosomes in Prokaryotes

NewsGuard 100/100 Score

Prokaryotes are the group of organisms including bacteria and archaea that do not have a membrane-bound nucleus and instead have a circular, double-stranded molecule of DNA called a nucleoid, that is not contained in a nuclear envelope. This prokaryotic chromosome may vary in size from 160,000 base pairs in the bacterium Candidatus Carsonella ruddii, for example, to up to 12,200,000 base pairs in the soil-dwelling bacterium Sorangium Cellulosum. Some bacteria such as Borrellia Spirochetes (which causes Lyme disease) contain a linear chromosome rather than a circular one.

Within the well defined nucleus of the eukaryote, chromosomes have a sequence-based and well defined structure, while in prokaryotes there is a single point from where replication starts. In archaea, however, replication may originate at multiple points. The non-bound nuclei found in prokaryotes do not have a well defined DNA structure organized around proteins, with the exception of the archaea where DNA is packaged to form nucleosomes. The nucleoid occupies a central position in the bacterial cell as the nucleus does in eukaryotic cells. However, unlike the nucleus, the nucleoid constantly undergoes structural changes.

The chromosomes within the prokaryotes are also found in the form of small molecules of DNA called plasmids. Since these plasmids can be found attached to the plasma membrane, they can be easily isolated in the lab by using centrifugation to create small pellets of the plasma membrane along with the DNA. Plasmids are generally super coiled like eukaryotic DNA and this needs to be uncoiled to allow for transcription and translation of proteins.

Earlier it was believed that prokaryotes only ever contained a single chromosome. Recently, however, the number of chromosomes in prokaryotes has been determined using DNA fragment mapping and pulsed-field gel electrophoresis techniques. Results show that the Vibrio species of bacteria that causes diseases such as cholera in fact contains two large, circular-mapping chromosomes.



Further Reading

Last Updated: Jun 22, 2023

Dr. Ananya Mandal

Written by

Dr. Ananya Mandal

Dr. Ananya Mandal is a doctor by profession, lecturer by vocation and a medical writer by passion. She specialized in Clinical Pharmacology after her bachelor's (MBBS). For her, health communication is not just writing complicated reviews for professionals but making medical knowledge understandable and available to the general public as well.


Please use one of the following formats to cite this article in your essay, paper or report:

  • APA

    Mandal, Ananya. (2023, June 22). Chromosomes in Prokaryotes. News-Medical. Retrieved on April 15, 2024 from

  • MLA

    Mandal, Ananya. "Chromosomes in Prokaryotes". News-Medical. 15 April 2024. <>.

  • Chicago

    Mandal, Ananya. "Chromosomes in Prokaryotes". News-Medical. (accessed April 15, 2024).

  • Harvard

    Mandal, Ananya. 2023. Chromosomes in Prokaryotes. News-Medical, viewed 15 April 2024,


The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of News Medical.
Post a new comment

While we only use edited and approved content for Azthena answers, it may on occasions provide incorrect responses. Please confirm any data provided with the related suppliers or authors. We do not provide medical advice, if you search for medical information you must always consult a medical professional before acting on any information provided.

Your questions, but not your email details will be shared with OpenAI and retained for 30 days in accordance with their privacy principles.

Please do not ask questions that use sensitive or confidential information.

Read the full Terms & Conditions.

You might also like...
Baylor study reveals role of newly inherited DNA variants in recessive diseases