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BIO311: Molecular Biology

Unit 3: Chromosome, Chromatin, and Nucleosome   DNA is packed into chromosomes in cells. The structure of the chromosome is constantly changing based on the metabolic activities within the cell. The degree of chromosome condensation is regulated by protein modifications and by the nucleosome remodeling complex.

Unit 3 Time Advisory
This unit should take you approximately 12.5 hours to complete.

☐    Subunit 3.1: 0.5 hours

☐    Subunit 3.2: 4.5 hours

☐    Subunit 3.3: 3.0 hours

☐    Subunit 3.4: 3.0 hours

☐    Subunit 3.5: 1.5 hours

Unit3 Learning Outcomes
Upon successful completion of this unit, students will be able to: - Describe the structure of the chromosome. - Discuss the role of histones in packaging eukaryotic DNA.  - Compare and contrast heterochromatin and euchromatin. - Discuss how the nucleosome remodeling complex regulates gene activity.  - Discuss the consequence of histone modifications in eukaryotes.

3.1 Definition of a Chromosome   - Reading: NIH: Genetics Home Reference's "What Is a Chromosome?" Link:  NIH: Genetics Home Reference's "What Is a Chromosome?" (HTML)
 
Instruction: Please study this page.  Please note that eukaryotes have their chromosomes in the nucleus, which is a membrane-bound subcellular organelle.  Prokaryotes have no subcellular organelles; their chromosomes are in their cytoplasm.

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  • Web Media: The University of Utah’s "Tour of the Basics: What Is a Chromosome?" Link: The University of Utah’s "Tour of the Basics: What Is a Chromosome?" (Adobe Flash)
     
    Instructions: Please watch this audio slide show (about 5 min).  Make a note of the definition of a chromosome and its importance in heredity in both humans and other species.
     
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3.2 Organization of a Chromosome   3.2.1 Bacterial and Eukaryotic Chromosomes   - Reading: NCBI Bookshelf: Lodish et al.'s "Organizing Cellular DNA into Chromosomes" Link: NCBI Bookshelf: Lodish et al.'s "Organizing Cellular DNA into Chromosomes" (HTML)
 
Instructions: Please study the "Most Bacterial Chromosomes Are Circular with One Replication Origin," "Eukaryotic Nuclear DNA Associates with Histone Proteins to Form Chromatin," and "Eukaryotic Chromosomes Contain One Linear DNA Molecule" sections on this page.  Please note that DNA interacts with basic proteins in the chromosomes; in eukaryotes these proteins are called histones.
 
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  • Web Media: BioSolution’s "Histones Animation" Link: BioSolution’s "Histones Animation" (Text and Adobe Flash)
     
    Instructions:  Please scroll down the page and watch this video (1 min).  Please note that the entire chromosome is condensed only during replication.
     
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3.2.2 Nucleosome Arrays   - Reading: NCBI Bookshelf: Lodish et al.'s "Organizing Cellular DNA into Chromosomes" Link: NCBI Bookshelf: Lodish et al.'s "Organizing Cellular DNA into Chromosomes" (HTML)
 
Instructions: Please study the "Chromatin Exists in Extended and Condensed Forms" section on this page, including the "Structure of Nucleosomes" and "Structure of Condensed Chromatin" subsections. Please note that DNA interacts with basic proteins in the chromosomes; in eukaryotes these proteins are called histones.
 
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  • Reading: John W. Kimball’s "The Nucleus" Link:  John W. Kimball’s "The Nucleus" (HTML)
     
    Instruction:  Please study the "Nucleosomes" section on this page.
     
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3.2.3 DNA Loop and Nuclear Scaffolding   - Reading: NCBI Bookshelf: Griffiths et al.'s "The Nature of Eukaryotic Nuclear Chromosomes" Link:  NCBI Bookshelf: Griffiths et al.'s "The Nature of Eukaryotic Nuclear Chromosomes" (HTML)
 
Instruction: Please read the "Higher-Order Coiling" subsection on this page.
 
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  • Reading: NCBI Bookshelf: Roland Foisner's "Dynamic Connections of Nuclear Envelope Proteins to Chromatin and the Nuclear Matrix" Link: NCBI Bookshelf: Roland Foisner's "Dynamic Connections of Nuclear Envelope Proteins to Chromatin and the Nuclear Matrix" (HTML)
     
    Instructions: Please read the "Introduction" and "Interactions at the Interface Between the Lamina and the Nuclear Scaffold/Chromatin" sections on this page.
     
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3.3 Heterochromatin and Euchromatin   - Reading: Stanford University: John H. Frenster’s "Ultrastructure and Function of Heterochromatin and Euchromatin" The Saylor Foundation does not yet have materials for this portion of the course. If you are interested in contributing your content to fill this gap or aware of a resource that could be used here, please submit it here.

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3.4 Nucleosome Remodeling Complex   - Reading: The Saylor Foundation's "Chromatin Modifications and Their Effects on Gene Expression" Link: The Saylor Foundation's "Chromatin Modifications and Their Effects on Gene Expression" (PDF)
 
Instructions: Read this text.

3.5 Histone Modification   - Reading: NCBI Bookshelf: Brown’s "Accessing the Genome" Link: NCBI Bookshelf: Brown’s "Accessing the Genome" (HTML)
 
Instructions: Please read the entire Section 8.2: "Chromatin Modifications and Genome Expression."
 
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