<p>CHAPTER 10 VIRUSES</p><p>✦ Chapter Overview</p><p>What are viruses? This is a question no doubt posed by students, teachers, scientists, and certainly by those who have contracted a serious viral disease such as rabies, polio, or AIDS. As we began to learn more about viruses, we seemed to uncover even more questions. As we conquered one viral disease, such as smallpox, another seemed to take its place. As soon as we knew something about basic structures, methods of replication, and methods of cultivation, new and even more strange particles appeared, such as the viroids and prions. With the discovery of oncogenes in living cells, the imagination was once again stretched to the limits in terms of the possible impact that viruses could have on all of us. The field of virology is always an exciting discipline. The first part of this chapter provides an overview of viral characteristics and classification. This is followed by a presentation of the methods of viral replication and cultivation. The last part of the chapter is devoted to the recently discovered prions and viroids followed with a discussion of the role and importance of viruses as teratogenic and cancer causing agents.</p><p>✦ Chapter Objectives</p><p> Describe the general characteristics, structural components, shapes, sizes, specificity, host ranges, and potential origins of viruses.  Explain how viruses are classified and then list and describe the major characteristics of each group of viruses.  Describe what is meant by emerging viruses and be able to give examples.  List and describe the five steps of virion replication.  Contrast the mechanisms of replication in virulent and temperate phages.  List and describe the steps involved in animal virus replication.  List and describe the different types of culture systems currently used to grow animal viruses.  Define the term teratogen, and briefly describe how viruses act as teratogens. (teratoma)  Describe the properties of viroids and prions.  Describe how viruses cause cancer and then define the term oncogene.</p><p>10-1 Online resources: Video - online A. Viral structures - http://www.britannica.com/eb/art-18532 This site provides video and sound that explains different components of viral structures. B. Phage video - http://www.britannica.com/eb/art-68574 This video goes through phage infection similar to the animation. C. HIV video with sound - http://www.tulane.edu/~dmsander/WWW/Video/HIV.mov This video goes through HIV replication, similar to the animation. D. The diversity of life – viruses video from BioEd online - http://www.bioedonline.org/presentations/viruses/presentation.cfm</p><p>2. Animations – online A. http://biology.about.com/library/blvirusanim.htm Bacteriophage - This site does an excellent job of showing how a phage infects a bacterium. Show this in class when going over the lytic cycle of bacteriophage B. http://www.whfreeman.com/kuby/content/anm/kb03an01.htm Retrovirus life cycle (HIV is a good example) - This site is great for showing the detail of viral infection. You can stop the animation at several points to discuss what is happening, and then continue on from there. The animation also does an excellent job of demonstrating the cell contribution (ribosomes, ER, and Golgi) to making the virions C. http://darwin.bio.uci.edu/~faculty/wagner/movieindex.html Herpes virus animations - Click on the first one (HSV structure) and you can walk through the animations, explaining to students what is happening as you go D. Howard Hughes Medical Institute BioInteractive animation on the viral lifecycle. Go to the following link and click on the animation - http://www.hhmi.org/biointeractive/disease/animations.html E. Cells Alive! site on HIV overview - http://cellsalive.com/hiv0.htm </p><p> Web Destinations</p><p> http://www.virology.net/garryfavweb.html This site is an extensive comprehensive resource for information about virology  http://www.virology.net/Tutorials.html This site has a few good tutorials concerning this chapter – “How Now Mad Cow” for understanding the early history of prion diseases, “A dose of the pox” to learn more about smallpox, “The Panama Puzzle” to learn more about yellow fever, and</p><p>10-2 “Virus Replication to learn more about specific viruses (although the link to HIV does not seem to be working as of this writing).  http://www.virology.wisc.edu/ This site presents links (click on “News & Links”), graphics (click on “Virus World” for images, animations, and databases), and recent research information about plant and animal viruses.  http://www.boehringer-ingelheim.com/hiv/art/art_videos.htm This site has some excellent videos on HIV. The first one is especially good at showing the infection of a cell by HIV  http://academic.evergreen.edu/projects/phage/ This interesting site presents information about bacteriophage biology and phage therapy.  http://www.tulane.edu/~dmsander/Big_Virology/BVHomePage.html This site provided by Tulane Medical Center is titles “The Big Picture Book of Viruses”. It is an excellent resource of visual materials and has links to other sites.  http://cellsalive.com/phage.htm This web site from Cells Alive! features bacteriophages and provides information and links to other useful sites.  http://student.ccbcmd.edu/courses/bio141/lecguide/unit3/viruses/prion.html This site provides good background (including definitions, figures, and articles) on viroids and prions.  http://www.life.umd.edu/classroom/bsci424/BSCI223WebSiteFiles/OncogenicViruses.htm This site is a table listing the oncogenic viruses and the diseases they cause.</p><p> Discussion Topics: ( ie potential essay questions)</p><p> What characteristics do viruses have that allow them to be identified as living organisms? What characteristics are used to indicate they are nonliving?  Why are there problems with emerging viruses? What types of conditions play a role in emerging viruses and what can we do to prevent them from causing too many problems?  Oncogenes apparently are found in all living cells. What role do they play in human cells?  Identify several important plant viruses. Are any beneficial?  Because prions such as those that cause kuru and scrapie take many years to cause disease, how do we know they even exist? What evidence supports their existence?</p><p>✦ Chapter Outline</p><p>I. General Characteristics of Viruses A. What are viruses? B. Components of viruses 1. Nucleic acids a. DNA b. RNA 2. Capsids a. Capsomeres b. Arrangements 3. Envelopes 10-3 a. Naked – no envelope b. Glycoproteins/spikes c. Advantages and disadvantages C. Sizes and shapes 1. Helical capsids 2. Polyhedral capsids 3. Complex capsids D. Host range and specificity of viruses 1. Host range 2. Viral specificity E. Origins of viruses</p><p>II. Classification of Viruses A. Basic methods 1. Host and organ affected 2. ICTV 3. Virus family and genus 4. Nucleic acid classification a. RNA 1. Single stranded or double stranded 2. Positive-sense or negative-sense b. DNA – single stranded or double stranded B. RNA viruses 1. General properties of RNA viruses 2. Important groups of RNA viruses a. Picornaviridae 1. Enteroviruses 2. Hepatoviruses 3. Rhinoviruses b. Togaviridae c. Flaviviridae d. Retroviridae e. Paramyxoviridae f. Rhabdoviridae g. Orthomyxoviridae h. Filoviridae i. Bunyaviridae j. Arenaviridae k. Reoviridae C. DNA viruses 1. General properties of DNA viruses 2. Important groups of DNA viruses a. Adenoviridae b. Herpesviridae c. Poxviridae</p><p>10-4 d. Papovaviridae e. Hepadnaviridae f. Parvoviridae </p><p>III. Emerging viruses A. Diseases 1. Polio 2. Yellow fever 3. Dengue fever 4. HIV 5. Hantavirus 6. Influenza mutations B. Causes 1. Role of air travel 2. Ecological changes and development 3. Changes in human demographics 4. Technology and industry 5. Microbial adaptation and change 6. Environmental changes</p><p>IV. Viral Replication A. General characteristics of replication B. Replication of bacteriophages 1. Phage therapy 2. Properties of bacteriophages 3. Replication of T-even phage a. Adsorption b. Penetration c. Biosynthesis d. Maturation e. Release 3. Phage growth and the estimation of phage numbers a. Growth curve (1.) Eclipse period (2.) Latent period b. Plaque assay (1.) Serial dilutions (2.) Bacterial lawn (3.) Viral plaques (4.) Plaque-forming units C. Lysogeny 1. General properties of lysogeny a. Temperate phages b. Lambda phage (1.) Prophage</p><p>10-5 (2.) Lysogenic conversion 2. Lysogenic cycle a. Medical significance b. Induction D. Replication of animal viruses 1. Adsorption a. Naked – capsid proteins b. Enveloped - spikes 2. Penetration a. Endocytosis/fusion b. Uncoating 3. Biosynthesis a. Biosynthesis in DNA animal viruses b. Biosynthesis in RNA animal viruses 4. Maturation 5. Release E. Latent viral infections</p><p>V. Culturing of Animal Viruses A. Development of culturing methods 1. Early history 2. Subculturing 3. Tissue/cell culture B. Types of cell cultures 1. Primary cell cultures 2. Diploid fibroblast strains 3. Continuous cell lines 4. Primary cell cultures 5. Embryonated chicken eggs C. The cytopathic effect </p><p>VI. Viruses and Teratogenesis A. Teratogens B. Viruses as teratogens C. TORCH series</p><p>VII. Virus-like Agents: Satellites, Viroids, and Prions A. Satellites 1. Satellite viruses 2. Satellite nucleic acids (virusoids) 3. Require helper virus 4. Most associated with plant viruses B. Delta hepatitis 1. General characteristics 2. Transmission</p><p>10-6 C. Viroids 1. General characteristics 2. Diseases 3. Transmission 4. Origins D. Prions 1. Diseases 2. General characteristics 3. Origins</p><p>VIII. Viruses and Cancer A. General terms B. Human cancer viruses C. How cancer viruses cause cancer 1. DNA tumor viruses 2. RNA tumor viruses D. Oncogenes</p><p>10-7</p>