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

The Discovery of Viruses The Nature of Viruses Bacteriophages Outline The Discovery of Viruses The Nature of Viruses Bacteriophages Cell Transformation and Phage Conversion AIDS The Future of HIV Treatment Disease Viruses Prions and Viroids 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. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

The Nature of Viruses Viral Structure - Core of nucleic acid surrounded by protein. 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.

The Nature of Viruses Viral Shape Helical (Rodlike or threadlike) Isometric (Icosahedron) Bacteriophages (phages) are viruses that infect bacteria. Some named as members of a “T” series. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

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

Genes translated into proteins by the cell’s genetic machinery. 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. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Bacteriophages 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. 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 (Temperate) Viruses 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. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Compromising the Immune System 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. 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. 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. viralRNA and reverse transcriptase left floating in cytoplasm. Double strand of DNA,complementary to RNA, produced. Viruses are released via exocytosis. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

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

Viral genes are readily re-assorted by genetic recombination. 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 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. i.e. – human papilloma virus

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

The Discovery of Viruses The Nature of Viruses Bacteriophages Review The Discovery of Viruses The Nature of Viruses Bacteriophages Cell transformation and Phage Conversion AIDS The Future of HIV treatment Disease Viruses Prions and Viroids Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

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