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Cell Nucleus Jessica Harwood Douglas Wilkin, Ph.D. Say Thanks to the Authors Click http://www.ck12.org/saythanks (No sign in required) To access a customizable version of this book, as well as other interactive content, visit www.ck12.org AUTHORS Jessica Harwood Douglas Wilkin, Ph.D. EDITOR Douglas Wilkin, Ph.D. CK-12 Foundation is a non-profit organization with a mission to reduce the cost of textbook materials for the K-12 market both in the U.S. and worldwide. Using an open-source, collaborative, and web-based compilation model, CK-12 pioneers and promotes the creation and distribution of high-quality, adaptive online textbooks that can be mixed, modified and printed (i.e., the FlexBook® textbooks). Copyright © 2015 CK-12 Foundation, www.ck12.org The names “CK-12” and “CK12” and associated logos and the terms “FlexBook®” and “FlexBook Platform®” (collectively “CK-12 Marks”) are trademarks and service marks of CK-12 Foundation and are protected by federal, state, and international laws. Any form of reproduction of this book in any format or medium, in whole or in sections must include the referral attribution link http://www.ck12.org/saythanks (placed in a visible location) in addition to the following terms. Except as otherwise noted, all CK-12 Content (including CK-12 Curriculum Material) is made available to Users in accordance with the Creative Commons Attribution-Non-Commercial 3.0 Unported (CC BY-NC 3.0) License (http://creativecommons.org/ licenses/by-nc/3.0/), as amended and updated by Creative Commons from time to time (the “CC License”), which is incorporated herein by this reference. Complete terms can be found at http://www.ck12.org/about/ terms-of-use. Printed: July 1, 2015 CONTRIBUTORS Doris Kraus, Ph.D. Niamh Gray-Wilson Jean Brainard, Ph.D. Sarah Johnson Jane Willan Corliss Karasov www.ck12.org C HAPTER Chapter 1. Cell Nucleus 1 Cell Nucleus • Describe the features and function of the cell’s nucleus. • Define chromosome. • Explain the role of the nucleolus. Where is your DNA? You may know that a criminal can easily leave DNA at a crime scene. How? DNA is found in every cell of your body. In each cell there is a nucleus, which is home to your DNA. So if a criminal has a cut, and blood is left at the crime scene, or a hair falls out and is left behind, then DNA will also be left at the scene. The Nucleus The nucleus is only found in eukaryotic cells. It contains most of the genetic material, or the DNA ( Deoxy-ribonucleic acid) of the cell. This genetic material inside the nucleus is like a set of instructions. These instructions tell the cell how to build protein molecules needed for the cell to function properly. The nucleus is surrounded by the nuclear membrane, a double layer that controls what goes in and out of the nucleus. The nucleus also has holes embedded in the nuclear membrane. These holes are nuclear pores, and they allow things to flow in and out of the nucleus. Chromosomes Inside of the nucleus, you will find the chromosomes. Chromosomes are individual strands of DNA wrapped around proteins. They contain genes, or small units of genetic material, that control many of the traits and characteristics you are born with. Human cells have 46 chromosomes in each cell except the sperm and egg cells (23 each). 1 www.ck12.org Nucleolus The nucleus of many cells also contains a central region called the nucleolus. The job of the nucleolus is to build ribosomes. These ribosomes flow out the nuclear pores into the cytoplasm. Ribosomes are the organelles where proteins are make in the cytoplasm. See the composition of the nucleus pictured below ( Figure 1.1). FIGURE 1.1 In eukaryotic cells, the DNA is kept in the nucleus. The nucleus is surrounded by a double membrane called the nuclear envelope. Within the nucleus is the nucleolus. Vocabulary • • • • • • • Chromosomes: individual strands of DNA wrapped around proteins DNA: nucleic acids that store an organism’s genetic code Genes: small units of genetic material that control many of the traits and characteristics you are born with Nucleolus: the job of the nucleolus is to build ribosomes Nucleus: a place in the cell that is surrounded by a membrane and contains the chromosomes Nuclear membrane: a double layer that controls what goes in and out of the nucleus Ribosomes: the only non-membrane covered organelle, it is found in all cells Summary • The nucleus contains the genetic material of the cell. • The genetic material of the cell is found in chromosomes, or DNA wrapped around proteins. • The nucleolus, which makes ribosomes, is also inside the nucleus. Explore More Use the resources below to answer the following questions. • Nucleus at http://www.youtube.com/watch?v=DMd3mr6rQ2o (2:25) 2 www.ck12.org Chapter 1. Cell Nucleus 1. What is chromatin? What molecules make up chromatin? 2. What is the nuclear membrane? What kind of membrane is this membrane? 3. What is the nucleolus? What molecules do you find there? Review 1. 2. 3. 4. What is contained in the nucleus of a cell? What is a chromosome? Where are chromosomes located? How many chromosomes do humans have? What is the function of the nucleolus? References 1. Mariana Ruiz Villarreal (LadyofHats), modified by CK-12 Foundation. Position of the nucleus inside a cell . Public Domain 3