Nucleolus | Biology | Britannica

Ask the Chatbot Games & Quizzes History & Society Science & Tech Biographies Animals & Nature Geography & Travel Arts & Culture ProCon Money Videos nucleolus Introduction References & Edit History Quick Facts & Related Topics Images Contents Science Biology Cells, Organs & Tissues

nucleolus biology Ask the Chatbot a Question More Actions Print Cite verifiedCite While every effort has been made to follow citation style rules, there may be some discrepancies. Please refer to the appropriate style manual or other sources if you have any questions. Select Citation Style MLA APA Chicago Manual of Style Copy Citation Share Share Share to social media Facebook X URL https://www.britannica.com/science/nucleolus Feedback External Websites Feedback Corrections? Updates? Omissions? Let us know if you have suggestions to improve this article (requires login). Feedback Type Select a type (Required) Factual Correction Spelling/Grammar Correction Link Correction Additional Information Other Your Feedback Submit Feedback Thank you for your feedback

Our editors will review what you’ve submitted and determine whether to revise the article.

External Websites

• National Center for Biotechnology Information - PubMed Central - The Nucleolus: Structure and Function

Ask the Chatbot a Question Also known as: nucleoli Written by Melissa Petruzzello Melissa Petruzzello is Assistant Managing Editor and covers a range of content including plants, algae, and fungi; insects and spiders; and renewable energy and environmental engineering. She also handles... Melissa Petruzzello Fact-checked by Britannica Editors Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree.... Britannica Editors Last updated Nov. 18, 2025 •History Table of Contents Table of Contents Ask the Chatbot

nucleolus, spherical body within the nucleus of most eukaryotic cells, involved in the synthesis of ribosomal RNA (rRNA) and the formation of ribosomes. Nucleoli appear shortly after mitosis and form around specific repeating chromosome regions, known as nucleolar organizing regions, within the nucleus. A single nucleus can house one to several nucleoli, depending on the organism and cell type.

The nucleolus contains the genes that encode rRNA. Each ribosome contains ribosomal proteins, which are synthesized in the cytoplasm, and at least one large molecule of rRNA and at least one small molecule of rRNA, which are synthesized in the nucleolus. To form new ribosomes, ribosomal proteins are transported to the nucleolus and there combined with the large and small rRNA molecules, creating the large and small subunits of the ribosome. These subunits are then returned to the cytoplasm for final assembly into functional ribosomes.

Plural: nucleoli (Show more) Related Topics: nucleus (Show more) See all related content

In addition to its importance in ribosome biogenesis, the nucleolus contains a number of proteins with no known role in ribosome formation, which suggests that the nucleolus may have additional functions. It is possible that the nucleolus plays a role in the regulation of mitosis and the progression of the cell cycle, and it is thought to be involved with the cell’s response to stress.

Melissa Petruzzello