1. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Viruses Chapter 33 Copyright © McGraw-Hill Companies Permission required for reproduction or display

2. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies The Discovery of Viruses Viruses possess only a portion of the properties of organisms.  Segments of DNA or RNA wrapped in a protein coat. - Must reproduce within cells.  Vary greatly in appearance and size.

3. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies The Nature of Viruses Viral Structure - Core of nucleic acid surrounded by protein coat (capsid).  Classified by nature of genomes. - RNA-based viruses - retroviruses.  Nearly all form a protein sheath or capsid around their nucleic acid core. - Many animal viruses form an envelope around the capsid. Host Range - Suitable cells for a virus.

4. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies The Nature of Viruses Viral Replication - Viruses can reproduce only when they enter cells and utilize host’s cellular machinery.  Genes translated into proteins by the cell’s genetic machinery. Viral Shape  Helical (Rodlike or threadlike)  Isometric (Icosahedron)

5. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

6. Bacteriophages Bacteriophages (phages) are viruses that infect bacteria.  Some named as members of a “T” series. Lytic Cycle  Tail fiber contacts lipoproteins of host bacterial cell wall. - Tail contracts and tail tube passes through opening in base plate, piercing bacterial cell wall.  Contents injected into host cytoplasm.

7. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Bacteriophages Lysogenic Cycle  Many bacteriophages integrate their nucleic acid into the genome of the infected host cell (prophage). - Integration of a virus into a cellular genome is termed lysogeny.  Lysogenic Cycle  Lysogenic (Temperate) Viruses

8. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Cell Transformation and Phage Conversion Transformation - Genetic alteration of a cell’s genome by the introduction of foreign DNA.  Phage Conversion - Foreign DNA contributed by bacterial virus. - Disease-causing bacteria Vibrio cholerae usually exists in harmless form.  Bacteriophage that infects V. cholerae introduces into the host bacterial cell a gene that codes for the cholera toxin.

9. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

10. AIDS Acquired Immunodeficiency Syndrome (AIDS) was first reported in the US in 1981.  Estimated over 33 million people worldwide are infected with Human Immunodeficiency Virus (HIV). Compromising the Immune System  In normal individuals, white blood cells patrol the bloodstream and attack invading bacteria or viruses.

11. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies AIDS In AIDS patients, the virus hones in on CD4 + T cells, infecting and killing them.  Without T cells, the body cannot defend against invading bacteria or viruses. - Each HIV particle possesses glycoprotein (gp 120) on its surface that precisely fits a cell-surface marker protein (CD4) on surfaces of macrophages and T cells.

12. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies AIDS After docking onto macrophage CD4 receptor, HIV requires second macrophage receptor (CCR5) to cross the cell membrane.  Once inside the macrophage, the HIV particle sheds its protective coat. - RNA and reverse transcriptase left floating in cytoplasm.  Double strand of DNA,complementary to RNA, produced.  Viruses released via exocytosis.

13. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

17. The Future of HIV Treatment Combination Drug Therapy  AZT and protease inhibitors - Keeps disease in check. Using A Defective HIV Gene  May reduce reproductive capability of HIV. Chemokines and CAF  Chemokines bind to and block receptors.  CAF Prevents viral replication. Disabling Receptors

18. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Disease Viruses Many human diseases are caused by viruses:  Influenza, Smallpox,Chicken Pox, Herpes May also play role in autoimmune diseases such as multiple sclerosis and diabetes. Influenza  Flu viruses are animal retroviruses distinguished by their capsid. - Types A, B, and C  Subtypes differ in protein spikes.

19. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Disease Viruses Recombination  Viral genes are readily re-assorted by genetic recombination. - Novel combinations of H and N spikes unrecognizable by human antibodies.  Inability to make perfect vaccines.  Flu Pandemics

20. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Disease Viruses Emerging Viruses  Viruses that originate in one organism and then pass to another and cause disease. - Ebola Viruses and Cancer  Viruses are capable of altering growth properties of human cells they infect by triggering oncogene expression.

21. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Prions and Viroids Prions  Infectious proteins that some believe may be responsible for transmissible spongiform encephalopathies. Viroids  Tiny, naked molecules of RNA that are an important infectious disease agent in plants.

22. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Copyright © McGraw-Hill Companies Permission required for reproduction or display