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Cell Nucleus
Jessica Harwood
Douglas Wilkin, Ph.D.
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AUTHORS
Jessica Harwood
Douglas Wilkin, Ph.D.
EDITOR
Douglas Wilkin, Ph.D.
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Printed: July 1, 2015
CONTRIBUTORS
Doris Kraus, Ph.D.
Niamh Gray-Wilson
Jean Brainard, Ph.D.
Sarah Johnson
Jane Willan
Corliss Karasov
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C HAPTER
Chapter 1. Cell Nucleus
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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).
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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)
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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
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