Connection lost. Please refresh the page.
Get help How to study Login Register
Ready to learn?
Pick your favorite study tool


Recommended video: Eukaryotic cell [18:45]
Overview of the cell and its contents.

The nucleolus (plural: nucleoli) is a dark-staining, typically spherical body within the nucleus of a cell. It is a dense non-membrane-bound structure which forms a specialized subdomain of the nucleus that is responsible for the synthesis of ribosomal subunits.

Each nucleolus is composed of an aggregate of ribosomal genes, newly synthesized ribosomal RNA (rRNA), ribosomal proteins and ribonucleoproteins. The densely concentrated rRNA that is complexed into ribosomal subunits is responsible for the intense basophilia (dark-staining) of nucleolus.

The main function of the nucleolus is to synthesize both small and large subunits of ribosomes. These ribosomal subunits are ultimately transported out of the nucleus into the cytoplasm, where they are assembled into ribosomes.

It is important to note that not all cells have a nucleolus and that the presence and number of nucleoli is an indication of the protein synthetic activity of a cell. Thus, cells such as nerve cells contain nucleoli whereas sperm cells have no nucleoli as they do not produce proteins. Additionally, the nucleolus may change in appearance depending on the functional state of the cell. For example, an inactive fibroblast will usually have a small nucleolus while a fibroblast activated during wound healing, for instance, has a prominent nucleolus.

Terminology English: Nucleolus
Definition Dark-staining, spherical body in the nucleus that produces ribosomal subunits
Aggregate of ribosomal genes, newly synthesised ribosomal RNA (rRNA), ribosomal proteins and ribonucleoproteins
Functions rRNA transcription and ribosomal subunits assembly

Test your knowledge on the histology of the eukaryotic cell with this quiz.

Learn more about the nucleolus and other components of the eukaryotic cell in the following study unit:

Nucleolus: want to learn more about it?

Our engaging videos, interactive quizzes, in-depth articles and HD atlas are here to get you top results faster.

What do you prefer to learn with?

“I would honestly say that Kenhub cut my study time in half.” – Read more.

Kim Bengochea Kim Bengochea, Regis University, Denver
© Unless stated otherwise, all content, including illustrations are exclusive property of Kenhub GmbH, and are protected by German and international copyright laws. All rights reserved.

Register now and grab your free ultimate anatomy study guide!