nucleoid

American  

[noo-klee-oid, nyoo-] / ˈnu kliˌɔɪd, ˈnyu- /

noun

1. the central region in a prokaryotic cell, as a bacterium, that contains the chromosomes and that has no surrounding membrane.

---

adjective

1. resembling a nucleus.

Usage

What is a nucleoid? A nucleoid is the central part of a prokaryotic cell that contains genetic material. A nucleoid is found only in a prokaryotic cell, such as a single-celled bacteria. It’s integral to reproduction and genetic behavior, housing chromosomes and DNA and, in some prokaryotic cells, additional DNA called plasmids. RNA and proteins can also be found within the nucleoid area. Nucleoid can be used to describe something that resembles a nucleus (a specialized mass of protoplasm encased in a double membrane). Example: If you examine the nucleoid of the bacteria, you’ll see that it lacks a specific chromosome related to that gene in similar organisms.

Etymology

Origin of nucleoid

First recorded in 1850–55; nucle(us) + -oid

Example Sentences

Most of these bead-like sections contain a nucleoid near the center, although the structures can also form without mtDNA present.

From Science Daily • Apr. 13, 2026

Therefore, they do not have a nucleus but instead generally have a single chromosome—a piece of circular, double-stranded DNA located in an area of the cell called the nucleoid.

From Textbooks • Jun. 9, 2022

Figure 10.2 Prokaryotes, including bacteria and archaea, have a single, circular chromosome located in a central region called the nucleoid.

From Textbooks • Jun. 9, 2022

They typically have cell walls enclosing cell membranes, cytoplasm, ribosomes and a nucleoid region with chromosomes.

From Textbooks • Jun. 9, 2022

Although the DNA of the nucleoid is associated with proteins that aid in packaging the molecule into a compact size, there are no histone proteins and thus no nucleosomes in prokaryotes.

From Textbooks • Jun. 9, 2022